Efficiently heating & cooling non-residential buildings. Themeninfo II/2016. Experiences with thermo-active building systems and heat pumps

Transcription

1 Themeninfo II/16 A compact guide to energy research Efficiently heating & cooling non-residential buildings Experiences with thermo-active building systems and heat pumps A service from FIZ Karlsruhe GmbH

2 2 BINE-Themeninfo II/16 Straight to the point The use of environmental energy to cool or, in combination with heat pumps, to heat non-residential buildings via thermo-active building systems (TABS) has established itself in recent years. The objective of such building and system concepts is not only to consume as little energy as possible in quantitative terms (low energy), but also to achieve the most optimal energy conversion in thermodynamic terms that takes the quality of the energy used into account (low exergy, LowEx ). Many successful and well-functioning examples show that with such systems a high degree of thermal comfort in combination with a high energy efficiency can be achieved. Various heating and cooling supply systems for this purpose are available on the market and the most important building simulation programs now have libraries with LowEx components to design these systems. For the planning and operation, product-specific documents as well as standards and guidelines are available. However, operational experience and the systematic scientific evaluation of a number of projects show that there are still possibilities within the planning, construction and operation phases for better exhausting the efficiency potential. What is often lacking is an optimal operational management of all sub-components as well as a critical analysis of the expended auxiliary energy. Furthermore, in practice this often raises questions as to the optimal control of the entire system in order to simultaneously ensure high efficiency and high workplace comfort. In a research project (LowEx:Monitor), 2 non-residential buildings were measured, investigated and evaluated in detail over a period of several years of operation. This yielded in a comprehensive cross-analysis of the performance of individual components and systems as well as the thermal indoor comfort and the overall system. The research project was funded by the German Federal Ministry for Economic Affairs and Energy as part of the energy-optimised building (EnOB) research initiative. The aim of this Themeninfo brochure is to provide guidance for optimising the interaction of ground source heating/cooling and thermo-active building systems as LowEx transfer systems in rooms. In addition, benchmark parameters for hydraulic subsystems and the overall system are also provided, which can be used during design, dimensioning and operation and also for quality assurance purposes. Your BINE editorial team wishes you an enjoyable read Content 3 The low-exergy concept 4 Thermo-active building systems 6 Thermal indoor comfort 8 Operating heat pumps efficiently 12 Operational management and control 14 Planning the integral building concept 1 En passant: Cooling concepts tailored to the climate 16 Implementation, commissioning and control 19 Check list In practice: Experience with three LowEx buildings Authors Dr.-Ing. Doreen Kalz, Fraunhofer Institute for Solar Energy Systems (FhG ISE) Prof. Dr.-Ing. Roland Koenigsdorff, Biberach University of Applied Sciences, Institute for Building and Energy Systems (IGE) With contributions from: Michael Bachseitz, Dr.-Ing. Robert Grob, Fritz Nüssle, Prof. Dr.-Ing. Jens Pfafferot and Dr.-Ing. Rita Steblow With the support of the following institutions: RWTH Aachen E.ON ERC, Zent-Frenger Energy Solutions, Unmüssig Projekt GmbH, DS-Plan Ingenieurgesellschaft für ganzheitliche Bauberatung- und planung mbh, Institut für technische Gebäudeausrüstung Dresden Forschung und Anwendung GmbH (ITG), Hochschule Offenburg Editors Dorothee Gintars, Uwe Milles Copyright Text and illustrations from this publication can only be used if permission has been granted by the BINE editorial team. We would be delighted to hear from you. Cover image: Biberach University of Applied Sciences Stefan Sättele All images are provided by the authors unless otherwise indicated. Lead photos: P. 3: Biberach University of Applied Sciences P. 4: Biberach University of Applied Sciences P. 6: Fraunhofer ISE P. 8: Biberach University of Applied Sciences P.12: Biberach University of Applied Sciences Stefan Sättele P. 14: Biberach University of Applied Sciences Stefan Sättele P. 16: E.ON ERC EBC, RWTH Aachen P. 19: Biberach University of Applied Sciences P. 21: DS Plan P. 22: UNMÜSSIG GmbH P. 23: Guido Erbring Kaiserstraße , 3113 Bonn, Germany Phone Fax kontakt@bine.info

3 BINE-Themeninfo II/16 3 The low-exergy concept In the German Energy Saving Ordinance (EnEV), the energy utilisation in buildings is assessed in purely primary energy terms, i.e. quantitatively. Low-exergy concepts go further: the thermodynamic qualities of the provided and utilised energy are harmonised with one other. The more the temperature level of the heat source corresponds with the use, the lower the exergy utilisation. Low-energy buildings with an energy-optimised overall concept encompassing the architecture, building physics and building services technology have a small heating and cooling energy demand. This can be achieved through a well-insulated and airtight building envelope, the consistently limited solar heat gain(for example, exterior solar shading systems), effective ventilation tailored to the hygienically required air change rates with heat recovery, sufficient thermal storage capacity of the building and limited internal loads (efficient office equipment, use of daylight). Such buildings can largely or even completely dispense with full air-conditioning and the use of chillers while still achieving a high degree of workplace comfort. They provide an ideal application for heating and cooling with thermo-active building systems (TABS), such as concrete core thermal activation or capillary tube mats, in combination with natural heat sources and sinks. The temperature difference between the indoor air and the heat sources for heating or natural heat sinks for cooling is lower than in conventional systems such as boilers with combustion processes. This therefore enables the exergy proportion of the supplied energy flow to be kept as low as possible: these are also known as LowEx systems. energy balances taking into account all energy conversion steps and the resulting losses. However, this is a purely quantitative approach. Although different forms of energy are assessed differently based on the primary energy factors, there is no comprehensive consideration of the thermodynamic qualities of the required energy flows. This is where so-called low-exergy concepts come into play. The intention is not only to reduce the respective quantities for the demand and supply but also to harmonise the respectively deployed energy qualities with one another. It is only when the quality is taken into consideration that the use of adapted heat sources and sinks is able to take full effect. While maintaining the necessary underlying conditions (e.g. thermal comfort), the exergy-based optimisation of supply concepts with the corresponding system components is aimed at minimising both the exergy destruction within a component or system as well as the external energy losses. This not only reduces the exergy requirement due to the lower demand for energy but also improves the use of the supplied exergy. Taking into account the energy quality Exergy describes the proportion of the total energy of a system or material flow which can perform mechanical work when it is brought into thermodynamic (thermal, mechanical and chemical) equilibrium with the environment. This means, for example, that a certain amount of thermal energy that is present at a high temperature level is more valuable than the same energy content at a lower level. This is because work can only be obtained from the difference to the ambient temperature. The exergy-based approach reveals this difference, while the purely energybased approach evaluates both cases the same. Currently, the evaluation of the energy utilisation in buildings is based on a consideration of the primary energy. Calculations of the primary energy requirement [EnEV 16, DIN V 1899: 13-] are based on the application of Fig. 1 Simple classification of exergy levels for energy sources and applications in buildings (Concept: IEA-Annex 49) Sources Exergy Application Oil, coal High Lighting Wind energy Electrical devices High-temperature waste heat, e.g. Medium Cooking from industrial processes (> C) Washing machines Low-temperature waste heat Low Domestic hot water e.g. from CHP plants and space heating ( C), geothermal energy

4 4 BINE-Themeninfo II/16 Thermo-active building systems (TABS) TABS can effectively utilise even the very small temperature differences between natural heat sinks or sources and the indoor temperature. The large, heat-transferring surface area of the thermally activated components enables significant thermal energy rates to be exchanged with the indoor space even with temperatures that are only slightly higher or lower. Thermo-active building systems (TABS) comprise all pipe systems for heating and cooling that are integrated into concrete components or other solid components, or which are integrated in plaster or screed applied to solid components without intermediate thermal insulation. They therefore make equal use of both the surfaces and thermal mass of the components. Particularly in office and commercial buildings, the ceilings and floors are almost exclusively thermally activated. The most typical and common example of TABS is provided by water-based, concrete core thermal activation (CCTA) systems where tube heat exchangers are cast into the concrete core of ceilings or floors. : A supplement to CCTA that has now proved itself in many buildings is provided by a piping system integrated near the surface of the concrete ceiling. A significant advantage of this system, which covers about -4 % of the respective space heating or cooling load, is that it enables better controllability of the indoor temperature in a room. The operating temperatures are strictly limited, however, when attempting to use TABS as LowEx systems. With CCTC, the supply temperature is normally at least 18 to C (cooling), with a maximum of 26 to 28 C (heating) (Fig. 3). These temperature levels are also a prerequisite for the so-called self-regulating effect, which occurs due to the Fig. 2 Experimentally determined steady-state heating and cooling capacities of water-based TABS with a K logarithmic temperature difference between the working medium and room, thickness of concrete slab: 28 cm. Design Concrete slab with directly Cavity floor applied screed on the concrete slab Coiled pipes Pipe spacing 1 cm, pipes Pipe spacing cm, on concrete slab in screed in the middle of the concrete slab Operation Heating Cooling Heating Cooling Total capacity [W/m²] Proportion of power output upwards [%] Proportion of power output downwards [%] dependence of the transferred thermal energy rate on the temperature difference between the component surface and room. With piping systems integrated near the surface of the concrete ceiling (so called edge strip elements ), higher operating temperatures of to 3 C are often chosen when heating. Limited thermal output The thermal output of a TABS depends on the position and spacing of the tube heat exchanger, the (logarithmic) difference between the water temperatures (supply and return) and the indoor temperature (Fig. 2, 4). Compared with a steady-state condition, dynamic peak loads that are temporarily higher can also be covered. However, this needs to be determined in relation to the specific building project, i.e. through simulations. The limited area-specific thermal power of TABS means that it is generally necessary to thermally activate the largest possible area in the room, whereby in practice the entire ceiling or floor area is never available for thermal activation. In particular, the possibilities for using suspended ceilings with sound absorber elements are severely limited in rooms with TABS. Space conditioning concepts with TABS can generally be divided into three system categories, whereby the heating and cooling functions of a system must not necessarily belong to the same category: 1. The TABS provides the complete heating or cooling function. Buildings exclusively cooled with TABS are typical. Heating is only suitable for uses with reduced comfort requirements (e.g. floor heating in warehouses). 2. The TABS is supported by an additional system in the building. This could, for example, be a mechanical ventilation system. It heats or cools the outdoor air possibly with seasonal adjustment to the desired (central) air inlet temperature (without a room control function). This reduces the heating or cooling capacity required by the TABS. 3. The TABS is combined with a heating or cooling system to provide individual peak load coverage (hybrid space conditioning system). In this case,

5 BINE-Themeninfo II/16 the TABS only covers the base load. Additional systems such as radiators, edge strip elements, heated/chilled ceilings or room-based controllable ventilation systems cover the peak load and regulate the indoor temperature. System categories 1 and 2 only enable a predefined tolerance range for the indoor temperature to be maintained. This is therefore also referred to as space tempering. It is only possible, however, to attain and maintain a specified value for the indoor temperature with an additional system (hybrid system according to 3). There are different performance requirements for the TABS in accordance with the system class: the performance requirements are explicit when a TABS provides the only cooling system in the room (system category 1). In this case, the resulting cooling loads need to be covered/managed solely by the TABS in accordance with the user requirements or, at the very least, it should be ensured that the defined limits for exceeding the comfort temperatures are adhered to. This initially seems sufficient for only a very few cases. A more detailed, dynamic consideration taking into account all constraints, such as the ventilation of the room, shows however that concrete core thermal activation in conventional office and school buildings (with coiled pipes positioned in the centre of the concrete ceiling) can certainly maintain the usual level of comfort for cooled spaces. In all other cases, the performance requirements for the TABS must be specified individually as part of the overall system planning and compared with its output capacity. In particular, the CCTC can also be used as a thermal storage system for time-shifting energy demand and generation. The heating or cooling of the supply air during periods when users are present and the operation of the CCTC are frequently separated time-wise by shifting the operation into the night-time hours. This makes it possible to reduce the thermal capacity of the heating and cooling generators, which saves investment costs and ensures a more uniform and higher system utilisation. However, this depends on there being a uniform space utilisation profile with specified usage times, so that the control when switching between user and reduced operation can be adjusted in accordance with the time delay for the transient heat transport (phase shift) from the concrete core to the room surface (via the so-called time constant for taking into account the thermal inertia). The advantages of TABS namely operating temperatures close to room temperatures and flexibility through storage and self-regulating effects are offset, however, by disadvantageous energy-related effects: the considerable thermal inertia and thus slower control capability, with the concomitant time differences between the signal change and room response, provide a disadvantage with flexible space utilisation profiles and can lead to over % more thermal energy being transferred to the room than with very swift and precisely controllable heating or cooling systems that allow rapid adaptation to changes in the usage times. The system-inherent low temperature differences in the 2 to K range require high mass flows and therefore considerable auxiliary energy for the circulation pumps. High energy and exergy efficiency is therefore only achieved when using TABS when the building/space conditioning/heating & cooling generation are correspondingly designed, constructed and operated as an overall system. Cooling capacity [kw therm ] Heating capacity [kw therm ] Specific power [W/m² TABS ] Useful heating energy [kwh therm /(m² month )] Day CCTA ESE ST-ESE ST-CCTA Day CCTA ESE ST-ESE ST-CCTA Fig. 3 Provision of a non-residential building with concrete core thermal activation (CCTA) and edge strip elements (ESE) in the office spaces. Heating and cooling capacity [kw therm ] and supply temperatures (ST) [ C] for the transfer systems, shown for a week in heating and cooling operation Pipe spacing [m] Heating Cooling Fig. 4 Steady-state heating and cooling capacity of a concrete core thermal activation system (total capacity upwards and downwards) with a K logarithmic temperature difference between the heating/cooling water and the spaces above and below in accordance with DIN EN 1377 (heat resistance method) Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep CCTA Radiator Mechanical ventilation system Fig. Heat provided in the building using concrete core thermal activation (supply with ground source heat pumps, temperature level /28 C) and radiators (district heating, temperature level 7/ C). As a fast responsive system at a high temperature level, radiators in this case cover most of the heating load and heat consumption, and significantly limit the use of the CCTA Supply temperature [ C] Supply temperature [ C]

6 6 BINE-Themeninfo II/16 Thermal indoor comfort High workplace comfort and user satisfaction are key concerns in the design of non-residential buildings. With adequate dimensioning, correct operational management and consideration of the operating limits of the TABS and the environmental energy sinks, cooling with TABS enables the indoor temperatures required in DIN 121 to be almost always maintained. Thermo-active building systems provide good prerequisites for high thermal comfort given by system and component temperatures close to the indoor air temperature, the high proportion of radiative heat transfer and the absence of a high air change rate and the concomitant high air speeds. Comfort investigations In the buildings investigated in the LowEx:Monitor project, the average operating indoor temperatures in summer range from 22. to 2. C, being considerably below the values measured in buildings using mechanical night User information and user satisfaction When starting to use a building, the users should be informed about the building and energy concepts and receive understandable instructions as to how they should and can behave in order to ensure high indoor comfort with low energy consumption and costs. A feature of convincing building concepts is that occupants are able to have a considerable influence. This demonstrably increases the satisfaction with the indoor comfort. User surveys also suggest that the users expectations regarding the indoor comfort conditions have a significant impact on their perception and satisfaction: informed users expect higher indoor temperatures in buildings with night-time ventilation and accept this. In buildings with water-based cooling using TABS, users have higher expectations regarding the indoor comfort and are therefore less satisfied with higher indoor temperatures. ventilation concepts. Even with increased outdoor temperatures with a running daily mean greater than 22 C, the maximum indoor temperatures are generally limited to a range between 27 and 28 C. The indoor temperatures vary only relatively slightly over the course of the day, i.e. in most buildings the average temperature rise during the period of occupancy between. and 2. kelvin (Fig. 6). To evaluate the thermal comfort, comfort category II was applied in accordance with DIN EN 121, i.e. a normal level of expectation which should be used for new buildings and renovations. In cooled office buildings, this corresponds to a maximum operative ( perceived ) room temperature of 26 C during the summer period, which may be exceeded for a maximum of % of the period of occupancy. This is maintained in most of the investigated buildings with the exception of a few individual hours (Fig. 7). Even in winter, the concrete core thermal activation in the buildings can ensure the required thermal comfort without additional heating systems, provided that the ventilation is carried out mechanically with heat recovery. The indoor temperature values rarely fall short of the minimum target value of C specified by DIN 121 (Fig. 6 is an example for a demonstration building). If the thermal indoor comfort according to these comfort criteria is insufficient in such buildings (Fig. 7, Class III or beyond the defined classes), this is often due to the following aspects: a change of use with higher internal loads, subsequently dispensing with solar shading, insufficient dimensioning of the heating/cooling systems and heat sinks, faulty operational management caused by, for example, increased supply temperatures, faulty activation of the cooling operation and simultaneous heating and cooling requirements within an operating day. In many of the buildings investigated, it was found that the indoor temperatures fell in some cases significantly violate the lower comfort limits during the cooling period (particularly at the beginning of the summer period) including periods with increased ambient temperatures (Fig. 7). Indoor temperatures in this range can be perceived by users as slightly cool. Outdoor and

7 BINE-Themeninfo II/16 7 Operative room temperature [ C] PMV model Running daily mean for the ambient air temperature 4 Temperature [ C] Occupancy during summer period [%] Weekend Day Ambient air temperature Indoor temperature Room 1 Indoor temperature Room 2 Periods of use Fig. 6 Thermal indoor comfort during occupancy in a demonstration building. Above: Hourly operative room temperature [ C] during occupancy, shown above the running daily mean for the ambient air temperature [ C] for two years of operation (comfort limits in grey). Below: Hourly operative room temperature [ C] for two selected offices and the ambient air temperature for a warm summer week. The periods of use are indicated with coloured markers. Occupancy during summer months [%] Building Class I Class II Class III Beyond Class III Fig. 7 Thermal indoor comfort during occupancy in the summer for the buildings investigated according to the comfort standard DIN EN 121 (exceedance of upper comfort limits only). Depicted is the percentage period of occupancy [%] when the requirements of comfort classes I III are met. Assessment according to the PMV comfort model (see Infobox, page 9). Water-based cooling of the buildings with TABS and environmental heat sinks. Each bar represents one year of a building. indoor temperature-dependent control can prevent the temperatures falling short of the comfort limits. In addition, the required thermal useful energy consumption is also reduced. The comfort analyses of the individual buildings during the summer do not show any marked differences with respect to the environmental heat sinks used in each case providing that the dimensioning is adequate and the operational management is reasonable. As heat sinks, the ground and groundwater are largely independent of the outdoor air temperature, and thus enable buildings to be cooled efficiently even at higher outdoor temperatures.

8 8 BINE-Themeninfo II/16 Operating heat pumps efficiently Originalgröße bitte bessere Vorlage Heat pumps require a heat source whose temperature level they raise to a useful level in buildings. Outdoor air, ground and groundwater are suitable as environmental heat sources or sinks. In summer mode, the latter can often also provide efficient direct cooling without an additional use of reversible heat pumps. A geothermal heat source and sink is particularly cost-effective for non-residential buildings with both, thermal heating and cooling energy demands. This is because the ground in many locations can be used both as a large-volume temporary storage as well as a heat source. If one source type is insufficient, then different sources can be connected in parallel to form a network. When choosing which concept to use, the sustainability and economic efficiency aspects should be taken into consideration. In summer, the environmental heat sink is primarily used for directly cooling buildings (solely with heat exchangers). Here electrical power is only required for the primary and secondary pumps for distributing cooling energy, but not for mechanical refrigeration. When heating, the natural temperature of the environmental heat source (soil: 6 to 14 C, groundwater: 8 to 12 C) only has to be slightly increased by the heat pump to the TABS necessary supply temperature between 26 and 32 C, which is therefore energy efficient. Fig. 8 Analysis of the heat pump systems when heating: (1, red) heat provided [kwh therm /(m²p.a.)], (2, yellow) seasonal performance factor (SPF) of the heat pump (compressor only) [kwh therm ], (3, green) seasonal performance factor (SPF) of the heat pump system (compressor, primary pump) [kwh therm ], (4, blue) fraction of the auxiliary electrical energy used for the primary pump relative to the total electricity used by the heat pump system [%]. 1: Heat delivered by heat pump [kwh therm : Efficiency of the heat pump, SPF [kwh therm ] (balance boundary HP) : Efficiency of the heat pump system, SPF [kwh therm ] (balance boundary II) : Proportion of the auxiliary electrical energy used by the primary pump [%] 2 1 Year Building A B C D H I J K L M N O

9 BINE-Themeninfo II/16 9 Fig. 9 Use of the subsurface ground as a heat source and sink, Left: Drilling holes for the borehole heat exchangers. Source left: Zent-Frenger GmbH Centre: Installing the pipes and right: Installed borehole heat exchanger Using environmental heat sources and sinks In 16 of the buildings investigated, the ground is deployed as an environmental heat source and sink using borehole heat exchangers between 42 and 1 metres in depth. The performance-related specific length of the borehole heat exchangers ranges between 1 and 19 metres per kilowatt heating capacity of the heat pump. The specific heat extraction rates are mainly dependent on the geological formations, water saturation and regeneration cycles. The outlet temperatures of the borehole heat exchangers range between 14 and C in summer and between 6 and 14 C in winter. Three buildings use groundwatercoupled heat pumps. The flow rates range between 11 and 7 m³/h. Prerequisites for efficient operation The energy efficiency of the environmental heat sources and sinks is determined by the auxiliary electrical energy and is therefore primarily dependent on the electrical power consumption of the primary pump (groundwater or brine pump) and its operating time. The analysis of the monitoring data shows that the correct design of the pipe network, the dimensioning of the pump and the operational management have a decisive influence on the energy efficiency of the environmental heat sink. A system operating with a high energy efficiency with an seasonal performance factor greater than kwh therm requires: an optimally designed pipe network with low pressure drops less than Pa/m, a correctly sized primary pump with an installed capacity less than 4 W el per kilowatt of thermal capacity of the borehole heat exchanger field or groundwater well, * all m² specifications in this BINE-Themeninfo refer to net floor area NFA or active component areas, unless otherwise stated. flow rate control of the primary pump in accordance with the temperature difference between the inlet and outlet (between 3 and kelvin) and optimal operational management (electricity consumption less than 2 kwh el /(m²p.a.)). * Thermal indoor comfort Thermal indoor comfort in non-residential buildings is assessed according to the European standard DIN EN 121:12-12, which defines two comfort models in accordance with the cooling concept being implemented: Adaptive: Buildings without mechanical cooling are assessed according to an adaptive comfort model that takes into account both changes in the outdoor climate and the influence of users on their immediate surroundings (e.g. opening windows, activating solar shading, no clothing requirements). Depending on the running daily mean for the outdoor temperature, the required target value for the indoor temperature is determined for three defined comfort classes. PMV: In accordance with the PMV (predicted mean vote) comfort model, buildings that are actively conditioned by both air-conditioning systems and thermo-active building systems should maintain stipulated indoor temperature target values regardless of the outdoor temperature conditions (Fig. 6). When concrete core thermal activation and environmental heat sinks are exclusively used for space cooling, system inertias and system-determined temperatures allow to maintain limit values for the indoor temperature, but not to guarantee stringent target values analogous to the PMV comfort model. If this has to be ensured, an additional, controllable and quickly responding cooling system is required. When designing the building, the thermal indoor comfort requirements and possibilities for user intervention should therefore be clearly defined.

10 BINE-Themeninfo II/16 Fig. Use of the surface-near ground as a heat source and sink, Left: Pre-installation of pipes prior to installing the baskets, Right: Drilling head, Source: Zent-Frenger GmbH The supply of consumers with different loads and operating times (TABS, ventilation system, server cooling) leads to partial load conditions during the operation of the geothermal system that can sometimes significantly reduce the energy efficiency (by to 4 %). However, this can be balanced out using a buffer storage system adapted to the different needs of the consumers. Investigations of the heating performance In the investigated buildings, the nominal thermal heating capacity of the ground-source electric heat pumps range between 4 and 322 kw therm. Six of these systems are operated monovalently; in ten buildings additional heat generators such as district heating, gas or pellet boilers are also used. In most of the buildings, buffer storage systems ranging from to 3, litres are incorporated, which corresponds to 4 2 litres per kilowatt of the heat pump capacity. In non-residential buildings, heat pumps are usually not used for domestic hot water production because very low hot water demand can generally be more economically met with decentralised generation. The economic operation is largely determined by the usage temperatures. Although the source temperatures by their very nature can hardly be influenced, a judicious selection of systems for supplying useful heat can have a considerable influence on not just the coefficient of performance but also the seasonal performance factor. If only the electricity used for the heat pump unit is considered, the investigated electrical heat pumps achieve seasonal performance factors between 2.4 and 6.6 kwh therm when heating, whereby most have a seasonal performance factor greater than 4 (balance boundary HP, Fig. 11 and 8). If the auxiliary power used for the primary pumps (balance boundary II, Fig. 11) is also considered, seasonal performance factors ranging between 2.3 and 6.1 kwh therm kwh el have been verified for the heat pump systems (Fig. 8). The primary pump requires between 6 and 28 % of the electricity used by the overall heat pump system, which means that depending on the system this has a significant impact on the overall efficiency. With most systems, the highest monthly performance factors were measured in autumn. This is because the ground is then regenerated by the (natural) cooling in summer and the buildings can still be heated with low supply temperatures. This requires a well set heating curve. In terms of the efficiency achieved (SPF), there are no clear differences between mono- and bivalent systems. The significant differences in the efficiencies of the investigated systems are mainly due to the different temperature differences between the primary and secondary circuits. These are determined on the primary side by the temperature level of the heat source and on the secondary side by the type of heating systems, their hydraulic layout and the operational management strategy. Within all of the projects, it is primarily attempted to achieve a heat supply at the lowest possible temperature level. The secondary-side temperatures in the heating circuit range between and 43 C on average; with three systems they even range between just 28 and 3 C (Fig. 3). With the heat pumps with borehole heat exchangers, the average temperature lift between the primary and secondary side therefore ranges between around and 3 K. If groundwater is used as the heat source, the average temperature lift only ranges between 1 and K given by the high temperature levels of the heat source, which remains almost constant throughout the year. The use and optimised operation of low-temperature heat transfer systems is a prerequisite for achieving highly energy efficient heat pumps. Analyses of the thermal hydraulics show, however, that not only does the heating circuit temperature setpoint for the particular consumers have an impact on the energy efficiency, but also the hydraulic connection of the heat pump, hot water storage and consumers.

11 BINE-Themeninfo II/16 11 Bivalent systems Hea ng Direct cooling Mechanical cooling Balance boundary III When a monovalent heat pump solution is not possible or desired, the ground-source heat pump can be combined with other heat generation systems to provide a bivalent solution. A variant frequently used in large buildings is the deployment of a geothermal heat pump system as a base load system, supplemented with a gas- or biomassfired peak load boiler. Depending on the position of the bivalence point, the base load system provides the main part of the heating demand required, whereas the peak load boiler provides the additional heating power on just a few (very cold) days. This variant benefits firstly from the higher supply temperature during peak load operation, which can be particularly important for areas equipped with radiators or convectors, and secondly from the low investment costs for the smaller sized ground source system as well as the heat generator as a whole. Investigations of the cooling performance In all the systems investigated, the environmental heat sink is primarily used, by means of heat exchangers, for directly cooling the building. In addition, space and air cooling is provided in six buildings using a reversible heat pump (thermal output between and kw therm ). The borehole heat exchanger field or groundwater well is then used as a heat sink for re-cooling. In the buildings investigated, the air conditioning cooling mechanically generated by the heat pumps contributes to between 16 and 6 % of the total annual cooling demand. Depending on the building and usage concept, direct cooling using borehole heat exchangers or groundwater wells makes it possible to provide space and air conditioning cooling with a high energy efficiency provided that there is careful design of both the hydraulics and the thermal capacity. For the geothermal system in the direct cooling operating mode (without the use of a reversible heat pump), seasonal performance factors (SPF) measured mostly were between and 18.8 kwht herm (balance boundary I, Fig. 11). Two systems even achieved efficiencies greater than 3. The SPF was less than with only five systems (Fig. 12). With active cooling supply using reversible heat pump operation, seasonal performance factors ranging between 4.8 and.8 are achieved for three systems. With two other systems, the operation during the first few years only achieved an SPF between 2. and 3.. The low exergy approach, i.e. supply/operation at a relatively high temperature level between 16 and C, should also be implemented when providing cooling with reversible heat pumps. However, with the two reversible systems with seasonal performance factors less than 4, the average temperature level in the secondary circuit lies between and 1 C. On the other hand, seasonal performance factors above are achieved for three other systems with average temperatures in the secondary circuit ranging between 1 and 19 C. Energy efficiency (SPF) Energy efficiency (SPF) Electricity Auxiliary energy consumption [kwh el HP Electricity 1 2 Nominal power of the primary pump [W el /kw therm ] Balance boundary II Balance boundary HP Balance boundary Fig. 11 Schematic depiction of the operating conditions: (1) Heating using a heat pump, (2) Direct cooling using an environmental heat sink (3) Mechanical cooling using a reversible heat pump. Additional depiction of the balance boundaries for the performance analysis of heat pump systems I III. rhp Electricity Ground water Ground Ground water Ground Fig. 12 Analysis of the cooling operation in the direct cooling operating mode (Balance boundary I, Fig. 11). Energy efficiency, expressed as a seasonal performance factor, shown relative to the auxiliary electrical energy consumption of the primary pump [kwh el /(m²p.a.)] (above) and the installed electrical nominal power of the primary pump [Wel /kw therm ] per kilowatt cooling capacity for the environmental heat sink (below).

12 12 BINE-Themeninfo II/16 Operational management and control The operational management and control of TABS in conjunction with heat pumps and the use of environmental energy present special requirements that differ from conventional systems. The controllers and control strategies usually used in building services systems cannot generally be used because these are designed for quickly responding heating and cooling systems. Because the CCTC and comparable TABS variants use large portions of the building mass as storage, their thermal time constants, i.e. the heating-up and cooling-down times, have the same order of magnitude as the building. Until now there has been no uniform approach to the operational management of such very inert systems. The main features of the operational management strategies employed to date are: Controlling the supply, return or average water temperature in accordance with the outside temperature. In most cases, a (running) mean is used, e.g. over 24 hours, in order to take the inertia of the TABS into account. Dead bands of the outdoor temperature when there is no TABS operation, or there is outdoor temperature-dependent disabling of the heating or cooling function to prevent frequent switching between heating and cooling. Different strategies for the operating times: a) (All-day) continuous TABS operation, b) Limited daily operation mostly night-time mode, which causes a shift in loads from day to night, and additionally: c) Temporary disabling of the circulation pumps after reaching a defined charge state for the TABS, e.g. as a function of the difference between the supply and return temperature, the level of the return temperature, or the average of the supply and return temperature, d) Time-controlled cycle operation of the circulation pumps: During the operation breaks, the temperature difference between the building component and water increases, which means that a greater thermal output is transferred during the operational phases than without interruptions. This shortens the required pump operating times. In addition, temperatures in or near the surface of thermally activated components, or indoor temperatures in one or more reference rooms, are occasionally incorporated in the operational management. In nearly all the operating strategies practised for very inert TABS, control strategies dominate relative to the use of preset usage profiles. However, although the recording of building component or indoor temperatures provides feedback in regards to the control situation, genuine indoor temperature control is not achieved. Another task that is usually solved individually with hybrid space conditioning is the integration of the peak load systems into the operational management and control concept. Design methods Apart from the basic choice of operating strategy, the choice of suitable parameter values for the supply temperatures and operating period is also important. Until now, this has been dominated by two approaches: semi-empirical settings based on the steady-state performance characteristics of TABS with testing and, if necessary, correction during operation, or thermal building simulations. Although the latter allows precise mapping of the dynamic system behaviour, they are relatively complex. A method for designing a CCTC system, which lies between steadystate interpretation and a detailed, individual simulation, is the unknown-but-bounded (UBB) method. Here the amount and temporal progression of the internal and solar heat gains do not have to be precisely known. Instead they are merely bounded by specifying the minimum and maximum progressions. The UBB method results in heating and cooling curves of the supply temperature for the CCTC system, which for each investigated zone depend on the running 24-hour mean of the outdoor temperature. These enable the specified indoor temperature range to be maintained or demonstrate that the given variability of the heat gains makes it impossible to comply with the comfort limits using just the CCTC system. This method provides a uniform, systematic approach to designing and operating concrete core thermal activation systems with supply temperature control.

13 BINE-Themeninfo II/16 13 Predictive operational management The thermal inertia of TABS also suggests the use of predictive operational strategies. These can be divided into three groups: Flow rate [m 3 /h] 2 1 Use of outdoor temperature forecasts in the aforementioned heating and cooling curves Multiple linear regression models: The heating and cooling energy requirements for the coming day are determined with linear regression models using outdoor temperature, solar radiation and internal heat load forecasts, and the TABS is then operated according to this prediction. This can lead to completely energycontrolled loading, i.e. the TABS is fed in advance over a limited period of time with precisely the expected amount of energy required and then, based on its storage capacity utilising the self-regulating effect, the TABS distributes this energy to the room throughout the day. Model predictive control (MPC): Based on forecast data (weather, occupancy, etc.), the system and control behaviour are simulated using a dynamic model parallel to the operation, whereby the control variables are continuously optimised. Core elements of the target function for the optimisation are typically the thermal comfort and energy use. Operational management and control of the plant In addition to the TABS itself, the control and operational management of the respective whole plant is also important for optimal operation. The hydraulic systems for TABS, heat pumps and geothermal systems generally require higher mass flow rates than conventional systems. The auxiliary energy required for the circulation pumps should therefore be minimised through optimal control and operational management. The power and energy limits of environmental heat sources and sinks such as groundwater and the ground are interdependent. With a borehole heat exchanger, for example, the cooling potential in summer depends on the heat extraction in the previous heating season. Furthermore, a lower extraction capacity enables greater energy extraction across the year and vice versa. Targeted energy management of the environmental heat source and sink can therefore be useful or even necessary. Larger buildings with TABS, heat pumps and environmental energy are operated possibly multivalent with multiple heating and cooling generators as well as several space conditioning systems. This usually leads to a large number of possible operating states and combinations that need to be covered by the building and plant control systems, which often requires individual strategies and solutions. Flow rate [m 3 /h] Energy consumption [kwh Temperature difference [K] Heating, Temperature difference [K] Cooling Fig. 13 Temperature differences [K] between the supply and return as well as the flow rates [m³/h] of the CCTC in heating and cooling mode for a year of operation. Heating Cooling % 9 % UBB OPT UBB OPT Secondary pump (south) Secondary pump (north) Primary pump Heat pump Fig. 14 Electrical energy consumption in heating and cooling mode split for the heat pump and the pumps in the primary and secondary circuit for a typical (UBB) and optimised (OPT) management strategy based on simulation calculations. The significant energy savings result from the reduction in the rotational speed of the circulation pumps under partial load. The power consumption of the circulation pumps correlates with the third power of the rotational speed. Source: Wystrcil et al 1. Energy consumption [kwh.

14 14 BINE-Themeninfo II/16 Design of integrated building concepts Buildings with thermo-active building systems in combination with the use of environmental energy only achieve considerable energy and exergy efficiency when the building, TABS and heat/cooling supply are considered holistically. This is why crucial decisions already need to be made during the design phase. A functional and efficient solution requires an integrally designed building approach where the useful energy demand for heating, cooling and ventilation is significantly reduced compared with conventional, e.g. fully air-conditioned buildings. An adequate planning process for this essentially comprises the following steps and features: Holistic harmonisation of the architecture, building physics and building services technology. Conception as a low-energy building. Fig. 1 The interactions in the entire system Thermal, hydraulic and control feedback Geothermal system Heat pump / Chiller Heat exchanger for direct cooling Cooling Storage system / Hydraulic separator Energy flows Building External & internal loads / Usage TABS Transmission & ventilation Heating Binding clarification and definition of the usage profiles for the building and the requirements for enabling flexible and variable use of the indoor spaces so that the possibilities and limitations for using TABS are clear from the outset. Early and clear definition of the target values for the indoor temperatures and the comfort classes to be observed in the individual function areas and the respectively tolerable deviations. Clarification of the natural energy resources available on the site, their temporal availability and capacity as well as the economic feasibility for exploiting them. Coordinating the performance requirements for the TABS and, if required, the additional systems in the respective rooms taking into account the requirements for controlling the room conditions; distributing the coverage of the output and energy requirements to TABS and additional systems. Preparing a control and zoning concept for the thermo-active building systems taking into account the strong dependencies between the capacity and demand coverage, operational management and storage due to the thermal inertia of the TABS. Coordinated, operationally and energy-optimised planning of the hydraulic systems for the heating/ cooling supply and the heating/cooling distribution. Coordination of the entire system, including the characteristics of the environmental heat sources and sinks (e.g. output and storage behaviour of borehole heat exchangers). These aspects need to be processed in terms of their interdependence and integration so that a holistic system design of the indoor and building climate, building services technology and energy supply is achieved. Incorrect assumptions in planning the hydraulics or the thermal design of the borehole heat exchangers or groundwater well system (e.g. regarding undisturbed ground temperatures or available delivery rates for groundwater)

15 BINE-Themeninfo II/16 1 En passant Cooling concepts tailored to the climate Fig. 17 shows the study results for a reference office building in summer in six European climates. To evaluate the planning aspects, the final energy demand for ventilation and cooling and thermal comfort are combined. Since some combinations do not lead to clear results, the investment costs are added as a third parameter. The calculated energy required for cooling typical office buildings increases from northern to southern Europe due to the higher outdoor temperatures and to a lesser extent the more intense solar radiation of around 22 to kwh therm /(m²p.a.). In northern Europe, internal and relatively high solar heat gains (long hours of sunshine when the sun is low) can be efficiently dissipated with cooler outdoor air by using natural ventilation during the day and night-time ventilation. Mechanically supported night-time ventilation improves the controllability and heat dissipation in midsummer. Active water-based cooling with natural heat sinks or compression cooling is only required when there are high comfort requirements or restrictions are placed on users (e.g. clothing requirements, no window openings). In central Europe, concepts with thermo-active building systems and environmental energy provide an efficient solution. If additional active cooling (e.g. a reversible heat pump) is required, thermally inert transfer systems can be used to shift Fig. 16 Mobile measurement equipment for recording indoor climate data at the workplace. loads. In order to maintain precise indoor temperatures, an additional controllable and quick-responding cooling system is required. In southern Europe, the long periods of hot weather with high temperatures mean that a relatively large cooling capacity is required. Because of the small temperature difference between the indoor spaces and natural heat sinks (outdoor air, ground), an active cooling system (e.g. compression cooling) is often necessary, and sometimes the dehumidification of supply air is also required. Fig. 17 Suitable cooling concepts (rated for energy efficiency, thermal comfort and investment costs) for various summer climate zones. 7 6 Temperature [ C] < Passive cooling Mechanical night-time cooling or radiant cooling systems with borehole heat exchangers (without chiller) Suspended cooling ceiling or concrete core activation with borehole heat exchangers as heat sink (generally realisable without chiller) Suspended cooling ceiling or concrete core activation with borehole heat exchangers as heat sink and chiller for additional cooling Suspended cooling ceiling with compression chiller and borehole heat exchangers as heat sink > 24 Suspended cooling ceiling or fan coil unit with compression chiller and cooling tower as heat sink and errors in the dimensioning will result in insufficient heating/cooling capacities and reduced energy efficiencies. These are almost impossible to compensate for or correct when operating the system. The installation of additional heating and cooling generators is then inevitable. Heat pumps should be carefully selected and sized for the specific application. Unnecessary safety factors for the capacity lead to a more frequent cycle rate, which adversely affects the efficiency and service life of the units. When selecting the manufacture or type, a maximum efficiency in the intended range of operating temperatures ( temperature lift ) should therefore be ensured here there are quite significant differences. Simulation supports design A thermo-hydraulic simulation of the overall system where the building, services technology, control and user behaviour are depicted in a closed simulation model enables the design alternatives and management strategies to be directly implemented into the models and makes it possible to observe the effects at the virtual level. This enables the interaction of all parameters to be evaluated in detail, which in addition to the building and system behaviour also include users, weather and control algorithms (Fig. 1). This in term makes it possible to develop, optimise and parameterise not just the planning but also the operational management strategies during the design phase.

16 16 BINE-Themeninfo II/16 Implementation, operation and control For the optimum operation of low-exergy systems, it must be ensured during commissioning that the open and closed loop control functions are implemented completely and correctly. Systematic monitoring during the operation then enables the consumption achieved in actual operation to be compared with the target values determined during the planning. LowEx systems in buildings can only achieve the target values for energy efficiency and thermal indoor comfort if all the individual components are properly matched. Here it is not just the quality of the components that is important but also the quality of the overall system. In this regard, LowEx systems differ significantly from conventional systems already established in building practice. For example, because the interfaces are clearly defined, the components used in conventional space cooling systems such as the cooling tower, chiller, cooling distribution and cooling transfer systems can be from different manufacturers. This is not readily possible with LowEx systems because the environmental heat sinks/sources and the building directly impact on each other. It is because the temperature levels on the source and sink side are predefined and cannot be actively adjusted. The correct design of the overall system, proper implementation on the construction site and, finally, reasonable operational management are decisive if the considerable efficiency potential offered by energy supply concepts using environmental energy is to be really exploited. So far, it has only been possible to implement and test the regulation and control programs once the systems have been installed. This means that the programming and commissioning of the building automation is often placed under considerable time pressure. This pressure is usually exacerbated by construction delays, so that the regulation and control functions can only be tested in accordance with the constraints applicable on the day if at all. This often leads to inadequate commissioning, resulting in suboptimal parameters and variations, or errors in the regulation and control functions. These only become evident, however, during operation. In addition to the reduced efficiency, this often also results in user complaints and higher operating costs. Emulation ensures control quality The emulation technique makes it possible to already check whether the operation and control strategies comply with the planning requirements, and whether all the functions are implemented correctly, before implementing of the control systems in the building. For this purpose, the control devices programmed with the regulation and control algorithms are integrated and tested in a virtual test environment. Based on simulations, emulation enables the regulation and control tasks to be systematically checked under realistic and reproducible conditions for all critical operating states, regardless of the currently prevailing weather and load conditions. This enables the operational and control behaviour of LowEx systems to be investigated independently of the construction progress, at an early stage and under different conditions, and compared with the planning and tendering specifications. The risks of malfunctions or unexpected building and system behaviour are therefore reduced. To achieve this, the following prerequisites and steps are required: 1. Clear design specifications: The operation and control processes should be described in the form of clear and comprehensible graphical control procedures before the programming begins. The graphic depiction enables gaps in the functions to be easily identified and eliminated. 2. Joint understanding of the regulation and control tasks: Prior to the implementation, the functions to be implemented should generally be jointly discussed by the designers and the building contractors based on verifiable and comprehensible documentation. 3. Identification of programming errors: Systematically checking the conformity of the operation and control programs with the previously created and determined control procedures as part of the emulation also enables minor program errors to be identified in advance. 4. Identification of parameterisation errors: The present emulation experience shows that parameterisation errors occur most frequently. The errors are difficult to detect in normal operation and, especially in terms of the energy efficiency, often have a serious impact.

17 BINE-Themeninfo II/16 17 Emulator Controller Emulated sensor values (outdoor temperature, supply and return temperatures, etc.) Recorded corrective and control signals (mean value of the outdoor temperature, activations, operational status, etc.) Fig. 18 Basic structure of the virtual test environment used for the emulation. Source: DS Plan Operation should be monitored Monitoring is recommended in order to ensure the beneficial and energy-efficient operation of the building and building services systems in the long term. This includes continuously recording and evaluating energy flows, demands (total energy consumption and individual partial loads), operating conditions and indoor environmental data, and the provision of information on the energyrelated status of the individual plants and systems as well as the overall system. Monitoring not only enables the operating results to be compared with the designed target values, but also allows valuable insights to be gained into the building s operation, especially during the first year. Currently, building automation systems usually provide data on the building s ambient temperature, the room conditions (indoor temperature, relative air humidity) as well as plant-specific parameters such as system temperatures and operating times. Thermal energy and electricity meters can additionally collect data on the heating and cooling consumption, the electricity consumed by individual units (pumps, fans) and the final energy consumption. The data enables a more targeted, energy-optimised operation of the building services equipment and if subsequently still possible system tuning of the individual components. The monitoring should be so detailed that the performance of the individual systems can be detected and possible causes of inefficiencies identified. At the same time, it must be sufficiently aggregated so that the cost of recording, processing, evaluating, visualising and storing the measurement data is reasonable in relation to the potential savings and so that the level of detail corresponds to the information needs of the users. A detailed measurement concept with appropriate devices and a concept for the data acquisition and archiving already need to be drawn up during the design and construction phase of the building and implemented Fig. 19 Parallel commissioning and quality assurance (QA) of the building automation (BA). Source: DS Plan Project start Date of handover Theory Operation BA commissioning and QA Usual practice??? QA with emulation Parallel" commissioning and QA of the BA Optimal operation Project start Pre-planning Preliminary design Detailed design Construction phase Commissioning and acceptance Date of handover

18 18 BINE-Themeninfo II/16 Fig. Left: Heating and cooling distribution in a laboratory building. Right: Electrical compression heat pump with a thermal output of 4 kw together with the designers of the building automation. Requirements for the level of detail and the scope of the recorded values, the accuracy of the sensors and meters, and the time intervals for the data acquisition should be clearly defined. A simple evaluation of the energy consumption of a building requires that the final energy carriers deployed are clearly assigned to the required energy services (e.g. space heating, cooling, etc.) based on the classification used in DIN V Only in this way it is possible to determine descriptive variables such as the heating or cooling energy consumption relative to the net floor area. Occupant satisfaction Under certain circumstances, the perceived indoor environment may not meet the expectations of occupants. Measurements make it possible, however, to provide objective data and to evaluate the thermal indoor comfort under operating and usage conditions, and thus assess the effectiveness of the cooling and ventilation concept. Frequently, significant data such as the indoor and ambient temperature values can already be gained from the building automation system. In addition, field measurements can be carried out with mobile monitoring equipment, which enable both indoor comfort parameters and user behaviour to be recorded. Assessing thermal comfort Both in planning and analysing operational data, the question arises as to how the thermal comfort can be evaluated in buildings with TABS and environmental heat sinks. Based on the specifications laid down in standards, the following procedure can be defined: Comfort model: For buildings with thermo-active building systems, the thermal comfort is principally assessed according to the PMV model in DIN 121. Usage periods: The indoor thermal comfort is investigated only during the period when users are present, e.g. weekdays from 8 am to 7 pm. Weekends, public holidays and vacation time are not considered. Scope of investigation: In the investigated building, selected (representative or critical) office spaces are assessed in design terms or measured and used for evaluating the thermal comfort. Seasonal assessment: The analysis of the thermal indoor comfort, i.e. the frequency with which the defined comfort classes I to III is exceeded, should be carried out for the entire summer period and not on a daily or weekly basis. A running daily mean value for the outdoor temperature of 1 C is recommended for the transition from the winter to summer period. Tolerance range for the comfort assessment: In the office spaces, the indoor temperature measured during periods of use during the summer period should not deviate by more than % of the limit values of the corresponding categories I to III in order to still maintain them. Comfort class for thermal indoor comfort: The indoor comfort is evaluated according to the defined upper and lower comfort classes I to IV. Depiction of results: The results of the measurement campaigns and planning are depicted in a comfort figure and thermal footprint (footprint for statistical data analysis). In the comfort figure (Fig. 6), the average hourly measured or simulated temperature of the reference spaces is shown above the running mean of the outdoor temperature in accordance with the required PMV comfort model. In addition, the graph shows the indoor temperature limit values for classes I to III. The thermal footprint shows the percentage period of use in summer during which the building complies with the upper limits of the thermal comfort categories I to III (Fig. 6, 7).

19 BINE-Themeninfo II/16 19 Checklist Energy-efficient heating and cooling supply using thermo-active building systems and environmental energy can be achieved if the following characteristics of these systems are used as factors for success during design and operation: 1. Storage capacity: The large storage capacity of thermo-active building systems enables a certain temporal decoupling between the energy demand and supply, extending, for example, to the overnight charging of buildings used during the daytime. This often makes it possible to reduce the capacity and to choose more favourable conditions for the heating/cooling generator and the environmental heat sources/sinks. However, this is partly countered by the limited controllability of TABS, resulting in the increased consumption of useful energy. 2. Operating temperatures: The operating temperatures of thermo-active building systems, i.e. low heating and high cooling temperatures, enable the use of efficient heating and cooling systems. It is only then that the greater useful energy consumption of TABS can be compensated for and an energy-efficient overall system achieved. 3. Energy-efficient heating and cooling: If reversible heat pumps and shallow geothermal energy are used to supply the TABS, this generally leads to a high energy efficiency. Seasonal performance factors measured at balance boundary II: Up to 6.1 kwh therm for the heat pump system, up to 18.7 kwh therm for the direct geothermal cooling and if required chillers with seasonal performance factors up to. kwhtherm/kw el in cooling mode. To utilise these features successfully, the following requirements apply for the design, construction and operation: 4. An adequate integral planning process with careful basic evaluation and consistently maintained specifications and parameters from the planning and construction to the operation.. Design and sizing of the TABS: Determination of the performance requirements for the TABS based on holistic system planning of the space conditioning in conjunction with any secondary systems. Dimensioning based on steady-state and dynamic processes, e.g. UBB method, simulation; planning and verification of the thermal and hydraulic zoning. 6. Design and sizing of the near-surface geothermal systems: Sufficient capacity and energy yield in feedback with the building s and plant s energy demands; consideration of the energy consumption of the groundwater or brine pumps. 7. Selection and sizing of heat pumps and chillers: Careful selection and dimensioning for the specific application, i.e. without unnecessary safety factors in regards to the capacity (avoiding frequent cycling with dynamic or strongly deviating usage profiles within a heating/cooling circuit, verification in regards to the economically reasonable integration of buffer storage systems with a concomitant reduction in peak loads, i.e. advantage of smaller heat pump/chiller sizing and improved electricity grid friendliness); choice of a product or type whose optimum efficiency is within the intended range of the operating temperature. 8. Energy optimised hydraulics: Because of the considerable mass flows required, the planning, design and execution of all hydraulic systems (primary, distribution and handover pipe networks) must be clearly aimed at achieving energy efficiency. This means: Low pressure losses, properly sized pipe networks (primary circuit is less than Pa/m and secondary circuit less than Pa/m), as well as correctly dimensioned pumps (primary pumps less than 4 W el /kw therm and secondary pumps less than W el /kw therm ). 9. The operational management and control should be integrated into the planning from the outset in order to correctly account for the dynamic thermal and energy behaviour of all subsystems. The choice of operational management and control during the planning, but also the later operation, can considerably influence the energy efficiency.. Operational monitoring and optimisation: Experience has shown that operational monitoring and analysis of the performance considerably contribute to reducing the energy consumption while ensuring the thermal comfort and thus the economic efficiency.

20 BINE-Themeninfo II/16 Aus In practice der Praxis Experience with three LowEx buildings over several years of operation Below, practical experience and operational evaluations will be presented for three non-residential buildings whose heating and cooling is carried out with LowEx systems using thermo-active building systems and environmental energy sources. In addition to the thermal indoor comfort, the heating and cooling supply systems were measured in detail using permanently installed measurement equipment over several years of operation. Although different architectural and design approaches were used for the investigated buildings, what they all have in common, however, is a correspondingly optimised overall concept that has significantly reduced the primary energy used for the building services equipment and lighting to below a limit value of kwh prim /(m²p.a). This is three times less than the value in currently typical non-residential buildings. Fig. 21 Building signatures for the heating mode (above) and cooling mode (below): Thermal comfort according to the PMV comfort model EN 121: Class II, specific useful heating and cooling energy consumption [kwh therm, energy efficiency of the heating and cooling supply (SPF, balance boundary II, Fig. 11) [kwh therm ] and the final energy consumption for the entire building for heating, cooling and ventilation. Thermal comfort: Percentage of occupancy periods when the class II comfort requirements are fulfilled. The arrows indicate the direction of the optimum. Thermal comfort class II [%] Efficiency, Balance boundary II (APF) Office building in Stuttgart Aim Measurement Final energy [kwh final Heating energy [kwh therm Thermal comfort class II [%] Efficiency, Balance boundary II (APF) Office building in Freiburg Aim Measurement Final energy [kwh final Heating energy [kwh therm Thermal comfort class II [%] Efficiency, Balance boundary II (APF) Office and laboratory building in Duisburg Aim Measurement Final energy [kwh final Heating energy [kwh therm Thermal comfort class II [%] Aim Measurement Thermal comfort class II [%] Aim Measurement Thermal comfort class II [%] Aim Measurement Efficiency, Balance boundary II (APF) Final energy [kwh final Cooling energy [kwh therm Efficiency, Balance boundary II (APF) Final energy [kwh final Cooling energy [kwh therm Efficiency, Balance boundary II (APF) Final energy [kwh final Cooling energy [kwh therm

21 BINE-Themeninfo II/16 21 Office building in Stuttgart Profile (evaluation for the 12 operation year) No. of storeys Heated net floor area (NFA) [m²] 2, A/V ratio [m 1 ].31 Solar shading Blinds, exterior U-value external wall [W/(m 2 K)].21 U-value windows [W/(m 2 K)] 1. g-value windows [-].8 Useful heat [kwh therm.6 Useful cooling [kwh therm 9. Heating final energy [kwh therm, Balance IV 18.3 Heating efficiency [kwh therm ], Balance II 3.6 Cooling final energy [kwh therm, Balance IV 1.7 Cooling efficiency [kwh therm ], Balance II.9 Thermal comfort in winter, class II [%] 99 Thermal comfort in summer, Class II [%] 98 The office building is monovalently supplied in the heating mode by an electric compression heat pump with an output of 68 kw therm. In summer, the building is cooled directly via borehole heat exchangers (BHE) field. With about 6 kw therm of power, the waste heat from the server rooms is also used for heating. The heating and cooling is transferred to the indoor spaces using concrete core thermal activation and edge strip elements near the facade. The ventilation is provided by a ventilation system with heat recovery and an additional heat exchanger, which pre-heats or pre-cools the fresh air. The air change rate per person is set at to 4 m³/h. Based on the measurement values, this results in an annual final energy consumption for heating of 17.2 (11) and 18.3 (12) kwh el /(m²p.a.). For the ventilation, a final energy consumption of.4 or 4.4 kwh el /(m²p.a.) was measured. The entire supply system is characterised by a very well and thoroughly designed hydraulic system. The electricity required for the primary and secondary pumps for heating and cooling amounts to 3. kwh el /(m²p.a.). This minimal auxiliary energy consumption in the primary and secondary circuits enables high energy efficiency. The primary circuit pump uses only % of the total electricity required for the heat pump system. The efficiency achieved for the heat pump system (balance boundary II) when heating has an SPF of 3.6 kwh therm. Fig. 22 Schematic depiction of the heating and cooling supply Heat recovery Near facade HP 68 kw therm BHEs, depth m Near facade Direct waste heat utilisation 2 kw therm Server Fig. 23 Energy efficiency evaluation: Provided heating and cooling energy [kwh therm /(m²p.a.)] and required electricity expenditure [kwh el /(m²p.a.)] for the water-based hydraulics and the electric heat pump and the energy efficiency (SPF) according to the following four balance boundaries (Fig. 11): (I) Use of environmental heat sources/sinks, (II) heat provision using heat pump or using direct cooling, (III) storage and distribution of heating and cooling energy and (IV) transfer of heating and cooling energy into the indoor spaces (operation year 12). Heating/cooling energy, electricity consumption, SPF Heating/cooling energy, electricity consumption, SPF I II III IV I II III IV Heating Electricity Efficiency (SPF) Cooling Electricity Efficiency (SPF)

22 22 BINE-Themeninfo II/16 In practice Office building in Freiburg Profile (evaluation for the 12 operation year) No. of storey 6 Heated net floor area [m²] 2,264 (part of the building) (investigated) A/V ratio [m 1 ].32 Solar shading Blinds, exterior U-value external wall [W/(m 2 K)].27 U-value windows [W/m 2 K] 1. g-value windows [-].8 Useful heat [kwh therm 1.9 Cooling [kwh therm 12. Heating final energy [kwh therm /(m²p.a.)], Balance IV 14.7 Heating efficiency [kwh therm ], Balance II 4.3 Cooling final energy [kwh therm /(m²p.a.)], Balance IV 1.2 Cooling efficiency [kwh therm ], Balance II 16.7 Thermal comfort in winter, class II [%] 97 Thermal comfort in summer, class II [%] 99 The office building is monovalently supplied in the heating mode by an electric compression heat pump with an output of 96 kw therm. A gas boiler is only used for supplying the common rooms and special use areas. In summer, the building is principally cooled directly via the borehole heat exchangers. The borehole heat exchangers have a depth of 1 m and are operated with an overall flow rate of 32 m³/h. Only a small proportion of the space and air cooling is provided by the reversible heat pump. The heating and cooling energy is delivered to the indoor spaces using CCTC systems. Near the facade, edge strip elements are installed about mm above the lower edge of the ceiling with a tube spacing of 8 mm. This enables the short-term supply and removal of heating and cooling loads, and thus quick and efficient temperature control. This concept also offers design advantages: radiators in the rooms are not necessary. Fig. 24 Schematic depiction of the heating and cooling supply Heat recovery Near facade HP 96 kw therm Ground floor 23 BHEs, depth 1 m Common rooms Boiler Near facade HP 24 kw therm 1 kw therm 4 kw therm Fig. 2 Provision of gas and electricity, use of shallow geothermal energy as a heat source and sink, heat generation using a heat pump and gas boiler, cooling and heating storage and transfer to rooms using concrete core thermal activation and edge strip elements. All information in kwh/(m²p.a.) The heating and cooling energy is delivered to the indoor spaces using concrete core thermal activation in the night-time mode and with edge strip elements near the facade in the daytime mode, whereby the supply temperature is variably controlled in accordance with the ambient temperature. When heating, the systems are operated at different temperature levels: the concrete core thermal activation between 26 and 28 C and the edge strip elements between and 34 C. The ventilation is provided by a ventilation system with heat recovery and a backup heat exchanger, which pre-heats or pre-cools the fresh air. Gas grid 1.6 Electricity grid Boiler HP

23 BINE-Themeninfo II/16 23 In practice Office and laboratory building in Duisburg Profile (evaluation for the 12 operation year) No. of storeys 3 Heated net floor area [m²] 4,27 A/V ratio [m 1 ].29 Solar shading Blinds, exterior U-value external wall [W/(m²K)].21 U-value windows [W/m 2 K] 1. g-value windows [-]. Useful heat [kwh therm /(m²p.a.)] 7.3 Useful cooling [kwh therm /(m²p.a.)]. Heating efficiency [kwh therm ] Balance II.6 (HP without district heating) Cooling efficiency [[kwh therm ], Balance II 16. /.8 / 12. (direct cooling/active cooling/ Efficiency of the overall cooling provision) Thermal comfort in winter, class II [%] 99 Thermal comfort in summer, class II [%] 98 In the inhaus2 research and demonstration building, a combined heating and cooling system was implemented, i.e. the generation of cooling energy with the simultaneous utilisation of the heating energy produced during the cooling generation, and vice versa. The combined heating and cooling system can, however, meet the heating or cooling requirements alone. The four operating modes are: Heating using a heat pump, direct cooling using heat exchangers, cooling using a reversible heat pump and dual operation, i.e. parallel generation of heating and cooling energy. The various operating modes are operated and controlled using the measurement and control technology integrated in the so-called centre plant. The heating and cooling energy is stored in buffer storage systems where the output and temperature are controlled for further distribution. The flow rate can be variably adjusted from 2 to 18 m³/h. A temperature difference-dependent flow rate control is implemented in the heating operating mode to achieve a temperature differential of 4 K and to reduce the electricity expenditure for the brine pump. The specific installed electric power consumption of the brine pumps in the primary circuit is 2 W el /kw therm. In the summer mode, 34 % of the cooling energy for the office and research areas and the servers is provided by direct cooling (via heat exchangers) and 66 % is provided using a reversible heat pump. The resulting temperature differences between the inlet and outlet of the borehole heat exchangers are on average 1.2 K in the direct cooling operating mode and 8 to 12 K in the compression cooling operating mode. The office area is supplied with heat in winter using concrete core thermal activation in combination with radiators or a supply and exhaust air system with heat recovery. Heat is provided by the groundsource heat pump for low temperature applications and by district heating for the high-temperature supply. The cooling is also achieved using concrete core thermal activation. Fig. 26 Schematic depiction of the heating and cooling supply Inlet temperature [ C] Heating/cooling [MWh therm /month] Building section 2 Building section 1 Building section 2 Building section Heat recovery 7 kw therm HP District heating 12 BHEs, depth 1 m Outlet temperature [ C] Conference Fig. 27 Depiction of the inlet and outlet temperatures of the borehole heat exchanger (BHE) field (balance boundary I, Fig. 11), separated according to the operation modes. Heating: BHE is the heat source; Cooling: BHE is the heat sink. The large temperature difference in the heating and compression cooling operating modes are due to the temperature-dependent flow rate control. The small temperature spreading in the direct cooling mode is due to the constant flow rate. Compression cooling Compression cooling HP Direct cooling Direct cooling 96 kw therm Heating Fig. 28 Provided heating and cooling [MWh therm /month] from the geothermal plant, divided according to the operating modes: direct cooling, cooling provision using reversible heat pump and heating. Heating