Dynamic Simulation of Thermal Behaviour of Sheraton Lisboa Hotel & SPA

Transcription

1 Dynamic Simulation of Thermal Behaviour of Sheraton Lisboa Hotel & SPA Bernardo Santiago Gonçalves This paper presents a study on energy consumption in a hotel building in central Lisbon. The energy consumption, from gas and electricity, was analyzed based on monthly consumptions and as a function of hotel occupancy and external conditions. Based on the annual energy consumption an energy efficiency index was calculated and compared with the limit set by legislation, allowing the conclusion that the building does not require a plan to rationalize energy. A further detailed analysis of energy consumption is carried with the aid of a dynamic simulation performed using a commercial program (Design Builder) associated with EnergyPlus. The total energy consumption is within 10% of the real value and the results show the division of consumption in the main equipments and identify the main heat loads. The implementation of some measures to improve the overall efficiency of the building are analysed including the cost and investment return, for chillers, boilers and implementation of energy conservation methods. Key Words: Energy Efficiency, HVAC Systems, Building Energy Simulation, Sustainable Energy 1 - Introduction The energy consumption in buildings represents an important part of the electricity energy consumption in Portugal. The electricity energy generation on the other hand is an important contributor to CO 2 emissions and therefore there are strong aims to promote energy efficiency in buildings and in Portugal the regulations for buildings (RCCTE and RSECE), applicable depending on the installed thermal capacity in buildings. For services using more than 25 kwt or with more than 1000 m 2 RSECE should be applied. The buildings in this case are required to have a periodic audit and an energy classification index is given in the certification process. The regulation introduces demands on maintenance services and installation of monitoring equipment to allow the building owner to identify their energy consumptions. The building energy classification is made through the assessment of energy efficiency indexes that are obtained performing a dynamic simulation of the thermal behaviour of the building under nominal conditions. The present work is a contribution towards the certification process that in an earlier stage requires the analysis of energy consumption based on historical data for existing buildings and the dynamic simulation of one year use of the building under real conditions. The values of the real energy consumption compared to target values may impose the implementation of an energy rationalization plan. The analysis of the results of the dynamic simulation further allows the identification of the potential for energy saving in both the energy use and the improvement of acclimatization systems. Following this introduction, the next section includes the building and the acclimatization systems installed. Then section 3 presents data on energy consumption and on the building utilization and discussion. Section 4 presents the results obtained for the dynamic simulation for the real building. Section 5 analyses the possible implementation of energy conservation measures. The final conclusions are summarized in the last section.

2 2 Building Under Study - Sheraton Lisboa Hotel & SPA Sheraton Lisboa Hotel & SPA, is a 5 star hotel, located in central Lisbon. The hotel is dated from the 70 s. Its whole structure is made of concrete and has a total of m 2 of useful area. Its facade has a total of m 2 glazing. It has a total of 34 floors, 27 with clients access. The building offers many services to its clients: a total of 358 bedrooms, 10 suites, 1 presidential suite, 2 restaurants, 2 bars, conference rooms, SPA & Fitness, heated outdoor pool and a restricted restaurant/bar Club Lounge. The hotel internal services are mostly located in floors -5 to -2. The technical areas where the HVAC equipment, equipment for sanitary water distribution, air-conditioning and pool treatment, are located in four main areas: central C, floor 3; Andar Técnico Inferior (ATI), floor 2; Andar Técnico Superior (ATS), floor 27 and building coverage. The comfort temperature range is chosen by Starwood, and it s between 22 ºC and 24 ºC. There are 3 main systems responsible for the acclimatization and air quality of the building. These systems are: HVAC system, heating system and cooling system. The building acclimatization in different areas is done by 2 distinct system types: all air and air-water. For the common areas, including conference rooms, restaurants, lobby, corridors, etc., a constant volume air system is used. In this case, the air is acclimatized in the air treatment unit (ATU) and is led to the area to acclimate. There is a total of 35 ATU, with air flow rate between 100 and m 3 /h, and the fans consume between 0.37 and 7.5 kw. In the case of acclimatization with air-water system, fresh outside air is captured, treated in a ATU, and is inflated in the room. The regulation of temperature is achieved using a fan coil unit with four tubes, that includes cooling and heating coils. The fresh air ATU have flow rates between 5400 and m3 / h, and their fans consume between 2.2 and 5.5 kw. The heating system of the building consists of five atmospheric boilers using natural gas with thermal capacity between 88 and 828 kw, heating water flow rates between 7.28 and m 3 /h. The cooling system consists of four chillers with maximum cooling capacity of 460 kw and a maximum water flow of 79.1 m 3 /h. 3 Data Collection and Analysis This section presents the analysis of energy efficiency indexes and also some of the measurements that were performed to evaluate the rate of ventilation and efficiency of the chillers. Based on the bills it was possible to determine the gas and electricity consumption of the past three years. Those values are presented in table 1 in Tonne of Oil Equivalent (toe) and were used to specify the IEE ref, actures, defined as the ratio between the equivalent primary energy consumption and the floor area (RSECE, 2006) Year Electricity (toe) Gás (toe) Total Average Table 1 Energy Consumption

3 The monthly values were analysed as a function of different parameters. The gas consumption during the heating season shows an increase with the number of day-degrees and in parallel a decrease of electricity consumption with a large scatter for the colder months. The hotel occupancy presents variations between 5 and 8 thousand rooms per month with lower values during winter and more variations during the rest of the year. Figure 1 presents the electrical energy and gas consumption as a function of the hotel occupancy. It is possible to verify that there is a correlation between the increase of electricity consumption and increased occupancy, that occurs when cooling is required. Figure 1 Energy consumption as function of the occupancy Based on data of energy consumption and occupancy, three energy efficiency indexes were calculated: IEE ref,facturas, IEE médio-ponderado e IEE dormidas, based respectively on total of bills, expected value averaged by activity and based on hotel activity measured in number of rooms. For IEE ref,facturas the value of 43,77 kgep/m 2 was obtained. Comparing this value with RSECE s reference value 60 kgep/m 2, it s possible to observe that the calculated value is lower and the legislation does not requires the need to implement a plan to rationalize energy. The reference value to compare from the legislation mentioned before is for a 4 or 5 star hotel. As there are several activities in the building another factor IEE médio-ponderado can be calculated based on the weighted IEE of each activity present in the building, and provided in RSECE. The value obtained was 58,98 kgep/m 2 and does not change the previous conclusion. The IEE dormidas is defined as the ratio of total primary energy consumption and the number of sleeps sold. The value obtained considering one person per room, 15,66 kgep/m 2, is higher than the one provided in RSECE, 15 kgep/m 2 but is lower if more than one person is considered on average per room, although this is not stored in the statistics. The flow rate of fresh air in rooms/suites and room s corridors, was mesured to ensure that they meet the levels required by regulation. Table 2 presents these values. Rooms/Suites (m 3 /h.occupant) Room s Corridors (m 3 /h.m 2 ) Measured 30,92 4,67 RSECE 30 5 Table 2 Measured Air Flow For rooms regulation is complied with, the same doesn t happen with the corridors where a deviation of 6% is observed, possibly justified by the large space of the corridors for high standard hotels.

4 The energy efficiency ratio (EER) of the chillers was measured based on an energy balance on the cooled water and the electricity consumption. The values obtained for the two main units were 2.0 a value that is about 35% lower than the value 3.1 when they were acquired. 4 Dynamic Simulation According to RSECE the energy classification is based on another energy efficiency index obtained from a dynamic simulation of the building under nominal conditions. To prepare this model for existing buildings real conditions should be considered and the actual energy consumption should be predicted with less than 10% error. The models to perform the simulation should satisfy the standard set in ASHRAE-140. In the present work the software DesignBuilder was selected to configure the model and parameters and the simulation was carried out using EnergyPlus. The modelling and simulation were consistent with the data collected. To adapt the model to reality as possible, specific templates were created for the walls and windows, taking into account the thermal properties of materials. The air change per hour (ach) was calculated as 0.75 ach from the ATU flow rates and a further minimum value of 0.15 ach (air change per hour) was considered due to the effects of wind and opening windows. Another common factor to consider is the metabolic factor, common to the whole building, selected as 0.90.Pre-defined schedules referring to occupancy, lighting and equipment for each different area of activity were used. Comparing these schedules, for the major areas, with the nominal schedules in RSECE, the largest discrepancy was found in room s schedules. Table 3 presents the values of electrical energy consumption, in MWh/year, applied in key areas in three simulations. Rooms Kitchens Restaurants Simulation Lighting Electricity Lighting Electricity Lighting Electricity Conference Lighting Rooms Electricity Other Lighting Electricity Table 3 Charges applied in model Table 4 presents a summary of the simulation results in the form of total values of electricity consumption, gas consumption, internal gains, fabric and ventilation and the actual values for gas and electricity consumption. Values are all in GWh.

5 Simulation Real Electricity Gas Internal Gains Fabric and Ventilation Table 4 EnergyPlus Output Results From the results of the first simulation it can be observed that the electrical energy and gas consumption were low compared to the real electrical energy and gas consumption. As the values were lower, the electricity consuming loads and domestic heated water (DHW) values were raised, and the construction material properties were changed, in order to get a value closer to the real one. In the second simulation the electrical energy consumption was already below a 10% difference. So the main concern was the gas consumption. For that, the DHW value was raised and the boiler efficiency was set lower. With those changes it was possible to get both, electrical energy and gas consumption, below a 10% difference from the real values. The internal heat gains are shown in figure 2. The analysis of the results shows the importance of the heat through the envelop and the ventilation that correspond to 34% and 46% respectively of the heat losses. The heat loss through the walls may be reduced by changing the building envelop but it is a complex measure to implement and it was not considered in the last major revision made in the building in Those losses are shown in figure 3. The reduction of the ventilation heat loss is also difficult to implement since ventilation has minimum requirements so the only possibility is to introduce heat regeneration. This possibility and others are analysed in the next section. Figure 2 Internal heat gains

6 Figure 3 Heat losses 5 Analysis of Possible Improvements Despite the IEE calculated compared with the reference were good indicators that the energy consumption of the hotel is not above the reference value, some possible improvements to save energy were analysed. Outdoor Heated Pool Cover The first case would be put a cover at water level, on the outdoor heated pool. The F-chart (FChart, 2010) software was used to simulate the heat loss and therefore the cost of heating the pool Based on CAP Coberturas (CAP Coberturas, 2010) budget, of 8,200 for a PVC cover drive mechanic, the payback time was estimated and is shown in table 5. There is no significant shading in the swimming pool and if it exists it increases heating consumption. Method FChart Shadding 0 % 50 % Payback Time 6,9 9,5 Table 5 Estimated Payback Time in years

7 Replacement of Chillers The second case would be to replace the chillers that operate an average of 12 hours per day throughout the year. Considering a value of EER for a new chiller from Trane with EER of 3.12 compared with the value of 2 for the two main existing units an annual saving of 22,442 was estimated. Based on the Trane (Trane, 2010) budget of to replace the 2 main chillers the estimated payback time was calculated as 3.85 years. Replacement of Boilers Since it was not possible to calculate the actual boiler efficiency, it was estimated that this is between 75% and 85%. The boilers are approximately 15 years old. Based on a budget given by Babcock-Wanson (Babcock-Wanson, 2010) of 49,660 to replace all the five boilers, table 6 presents the annual savings and estimated payback time. Efficiency (%) Annual Savings ( ) Payback Time (years) , Table 6 Annual savings and payback time Thermal Use of Rejection Air The installed ATU have no means to recover heat from the rejected air, so a study was done to estimate what would be the gains and savings. For this study the four fresh air ATU responsible for the bedrooms acclimatization and fresh air were considered. Considering that only 50% of the calculated value can be used, are presented in table 7 the heating gains, cooling gains and annual savings. No budget was obtained for the installation of the heat recovery equipment and the implementation of the system is complex due to the distance between the inflation ATU and the extraction air fans. Heating Cooling Estimated Value (kwh) , % of Estimated Value (kwh) ,7 794 Savings ( ) 495,6 28,7 Table 7 Thermal Use of Rejection Air Thermal Solar Panels for Heating DHW The installation of solar panels is another solution with the potential to be taken into account. The goal would be the installation of about 25 m 2 of panels on the building s coverage, the only area available for such, to assist the heating of DHW, thereby removing a portion of the load of the boilers. Verdesolar presented a budget for panels of vacuum tubes to work in a primary circuit. Table 8 presents the heating capacity of those panels, compared to RCCTE value and a value calculated in FChart, simulating the same system. The values obtained from RCCTE are for a reference panel by default with much lower efficiency so its values have to be interpreted with care (ADENE, 2009).

8 Heating Capacity [(kwh/year)/6m 2 ] Heating Capacity RCCTE [(kwh/year)/6m 2 ] FChart [(kwh/year)/6m 2 ] Table 8 Budget, RCCTE and FChart for solar panels heating capacity Table 9 presents the budget given by Verdesolar, the annual savings and the estimated payback time. Budget for 24 m 2 ( ) Annual Savings ( ) Payback Time (years) ,9 Table 9 Budget, annual savings and payback time Replacing the Insulation of the DHW Deposits The exchange of the insulation of the deposits of DHW was another measure taken into account, either due to advanced age of some of the deposits and their insulation, as well as the demand for a better and more effective solution. Table 10 presents the areas and thickness of the existing insulation made of rock wool with conductivity of 0.04 W/mK. Based on these values, the value of annual losses and a boiler efficiency of 80%, the cost that these losses represent is estimated and included in the table. The overall value of the losses represents about 0.5% of the heat consumption and a replacement of insulation could reduce only part of this. Capacity (l) Area (m 2 ) Esp (m) Annual Losses (kwh) Annual Cost ( ) ,57 0, ,5 371, ,25 0, , , , ,6 Total ,5 815,9 Table 10 Analysis of thermal losses and annual cost of the DHW deposits 6 Conclusions This work presents an energy balance to a high standard hotel and its relation to the standards set in the Portuguese legislation. The ventilation in the rooms is within the legislation with a small deviation in the corridors. The energy consumption is within the limits for existing buildings and therefore there is no obligation to introduce a rationalisation plan. Nevertheless the economic exploitation is important and several measures are discussed. The larger benefits may be achieved by the replacement of the thermal equipment (chillers and boilers) with payback times below four years. Other measures such as to cover the external swimming pool, installation of solar panels and heat recovery of rejected air are more difficult to quantify and the payback times are larger than six years and the impact on the energy consumption are small. The energy classification of the hotel requires a dynamic simulation to be carried out in nominal conditions. A model was set up and used to simulate the real hotel conditions with a deviation below 10%. The results from the model show the important contribution from the heat loss through the building envelop and the contribution from ventilation that cannot be reduced.

9 7 References AP Coberturas (2010). Junho 2010; Babcock-Wanson (2010). Agosto 2010; RCCTE (2006) Decreto-Lei n.º 80/2006 de 4 de Abril (Regulamento das Características de Comportamento Térmico dos Edifícios); Despacho n.º 11020/2009 (Método de Cálculo Simplificado para a Certificação Energética de Edifícios Existentes no âmbito do RCCTE); F-Chart (2010) Julho 2010; RSECE (2006) Decreto-Lei n.º 79/2006 de 4 de Abril (Regulamento dos Sistemas Energéticos de Climatização em Edifícios); Trane (2010). Agosto 2010.