St Loyes Extra Care Facility PHPP Pre-Assessment Report

Transcription

1 St Loyes Extra Care Facility PHPP Pre-Assessment Report Gale & Snowden Architects & Engineers July 2011

2 Gale & Snowden Architects St Loyes Extra Care Facility PHPP Pre-Assessment Report Page 2 of 10 St Loyes Care Home PHPP Pre-Assessment Report Prepared by: Checked by: Project: Tomas Gärtner Maria Gale/David Gale St Loyes Care Home Version: Final Date: July 2011 Job No: B1103 Reference: Projects\Current\B1103 St Loyes Care Home \Reports & Specs Rev No Comments Date This document has been produced by Gale & Snowden for the St Loyes CCA project and is solely for the purpose of outlining the results from the initial PHPP modelling of this project. It may not be used by any person for any other purpose other than that specified without the express written permission of Gale & Snowden. Any liability arising out of use by a third party of this document for purposes not wholly connected with the above shall be the responsibility of that party who shall indemnify Gale & Snowden against all claims costs damages and losses arising out of such use Gale & Snowden Architects Ltd 18 Market Place Bideford Devon EX39 2DR T: F: Company No VAT Registration No

3 Gale & Snowden Architects St Loyes Extra Care Facility PHPP Pre-Assessment Report Page 3 of 10 Executive Summary This report illustrates the key findings of the PHPP pre assessment for the St Loyes Extra Care Facility project modelled under current weather conditions and also future weather data provided by Exeter University s Prometheus project. Main Findings All three construction methods will result in Passivhaus compliant designs for space heating demand, primary energy demand and overheating, when modelled with the current weather file, and without a requirement for additional shading. The heavy weight construction without additional shading performs better with regards to overheating and will result in a lower daily temperature swing from solar gains than the light weight or medium weight approach. The effect from devices that control solar gains in summer and also adequate ventilation appear to have a greater impact on reducing overheating in summer than thermal mass. If a successful strategy to control solar gains in summer can be implemented (e.g. overhangs and/or shutters) then a natural ventilation strategy via opening windows is sufficient to limit overheating in summer to acceptable levels for all four weather scenarios and independent from the method of construction.

4 Gale & Snowden Architects St Loyes Extra Care Facility PHPP Pre-Assessment Report Page 4 of 10 Contents Executive Summary... 3 Contents Introduction This Report Thermal Assessment & Calculation Heat Loss Methodology Building Fabric and Mechanical Design PHPP Passivhaus Standard Weather Files Shading Thermal Mass Ventilation Conclusions PHPP Pre Assessment Overheating Space Heating Demand... 9 References... 9 Appendix A Results Matrix... 10

5 Gale & Snowden Architects Ltd St Loyes Care Home PHPP Pre-Assessment Report Page 5 of Introduction 1.1 This Report The purpose of this report is to illustrate the key findings of the PHPP pre assessment for the St Loyes Care Home project with regards to overheating, space heating demand and specific primary energy demand. It assesses the initial designs for compliance with the Passivhaus standard. Furthermore various shading and construction methods with regards to the inclusion of thermal mass have been modelled under current and future weather data for the years 2030, 2050 and 2080 to assist the design team in developing a climate change adaptation strategy. 1.2 Thermal Assessment & Calculation The building design has been modelled using the Passivhaus Planning Package (PHPP). The PHPP is a design tool allowing specialist planners to assess and calculate the energy demand for low energy buildings. It was developed using dynamic simulations [AkkP 13] that were then validated by monitoring results of completed Passive Houses over the last 20 years. The result is a simplified model which pairs reliable results with justifiable effort for data acquisition [Feist 1994]. The Passive House Planning Package (PHPP) provides tools for: calculating energy balances (including U-value calculation) specifying and designing windows designing the comfort ventilation system determining the heating load estimating the summer comfort design the heating and hot water supply Whilst the PHPP has been utilised as a design tool for this project, this information is also valid as an initial assessment to show compliance with the Passivhaus Standard. 1.3 Heat Loss Methodology The heat loss methodology used for the simulation is as follows: The method is based on calculations of monthly energy balances It treats the whole building as one zone It takes into account internal casual gains and solar gains. It takes into account building orientation and properties of the materials used It utilises local weather data Using the above methodology the PHPP allows for predictions of annual space heating demand, heating load and frequency of overheating in summer. 1.4 Building Fabric and Mechanical Design It is understood that the project is still at outline planning stage and that no detailed design has been worked up to define the construction of the building fabric. Therefore all simulations have been prepared on the basis of the following recommendations and assumptions which are all based on good practice guidance from the Passivhaus Institute. All modelling results will need to be verified at a later design stage when more accurate information is available to confirm the performance of the actual building fabric design. Building Fabric Design A passive design strategy is to be followed including super insulation, high levels of air tightness and high performance triple glazed windows and doors: U-values Walls 0.15 W/sqmK Floor 0.15 W/sqmK Roof 0.1 W/sqmK Windows 0.85 W/sqmK (installed) Doors 0.85 W/sqmK (installed) Thermal bridge free design Glazing g-value = 0.5 U value = 0.58 Air tightness 0.6 ac/h

6 Gale & Snowden Architects Ltd St Loyes Care Home PHPP Pre-Assessment Report Page 6 of 10 Ventilation Efficiency >85 % Electric Efficiency <0.3 Wh/m³ short cold duct runs <1.5m per duct 100mm air based insulation to cold ducts For summer time ventilation the following strategy has been assumed: Summer Night ventilation Cross ventilation Windows tilted all night Summer Day time ventilation Cross ventilation All windows tilted for 6hrs/day Domestic Hot Water 3 No central gas boiler located in a plant room on 3rd floor above each entrance area Flow and return distribution with 24h circulation 25mm air based insulation to pipes No solar hot water Space Heating Decentralised direct electric Electricity Demand Clothes drying with clothes line Electric cookers 100% energy efficient lighting Drawings Floor plans revision 30/03/2011 Site plan revision 30/03/2011 Site sections revision 30/03/2011 Weather Data Exeter current weather data provided by PHI Exeter 2030 weather file based on Prometheus data for high emission scenarioa1fi, 50percentile, TRY Exeter 2050 weather file based on Prometheus data for high emission scenarioa1fi, 50percentile, TRY Exeter 2080 weather file based on Prometheus data for high emission scenarioa1fi, 50percentile, TRY 2.0 PHPP 2.1 Passivhaus Standard The Passivhaus methodology was established in the early 1990s and has since become the world leading standard in energy efficient design and construction. Today more than 35,000 buildings including dwellings, schools, offices and sport halls have been built to the Passivhaus standard. Detailed research and scientific monitoring on these projects have proven that using the Passivhaus methodology will reduce the energy demand of a building by up to 90% of that of a standard UK building (if built to current Building Regulation requirements). 2.2 Weather Files Weather files provided by Exeter University s Prometheus Project have been converted for use in the PHPP. Cooling load data at this moment in time was only available for the current weather file but not for future weather files. This will inevitably have an effect on the accuracy of the results, however, it is expected that the tendency of the results will remain similar and that the data is sufficient for a qualitative comparison between the different scenarios. 2.3 Shading Three different shading scenarios have been modelled for three different construction methods with the ventilation strategy always remaining the same. The building has been modelled with no shading, shading provided by balconies along the south facing elevation and with balconies and additional flexible shutters to the south facing elevation. 2.4 Thermal Mass The inclusion of mass in the construction of space defining building elements can help to stabilise internal temperatures by balancing out daily temperature swings i.e. the energy is stored in the solid walls, floors and ceilings before it heats up the space. The frequency of overheating events decreases significantly as the storage mass accessible from the room is increased.

7 Gale & Snowden Architects Ltd St Loyes Care Home PHPP Pre-Assessment Report Page 7 of 10 Therefore a heavy weight construction with solid external /internal walls, ceilings, floor and roof will perform better than e.g. a lightweight timber frame building. 2.5 Ventilation Mechanical ventilation with heat recovery (85%) efficiency has been allowed for in the winter months and natural ventilation via manually opening windows for summer ventilation. The average daily air change rate was estimated using the calculation procedure included in the PHPP. The air change rate is calculated based on size, location and type of opening (i.e. fully open or tilted), wind speed, temperature difference and hours of opening. The wind speed and temperature difference was established by following guidance from the PHI i.e. for daytime the wind speed is set at 2m/s with 4K temperature difference for night time ventilation the wind speed is set at 1m/s with 1K temperature difference. Location and size of windows was defined by the design with the assumption that all windows are openable and allow for cross ventilation. For night time ventilation it was assumed that all windows are tilted during the night. For daytime ventilation all windows were set to be tilted for 6 hours in the morning when outside temperatures are considered to be lower and windows are closed in the afternoon. The average daily ventilation rate resulted in 0.5 air changes for daytime ventilation and 0.2 for night time. Surveys on actually measured ventilation rates for naturally ventilated Passivhaus buildings in Germany support these results (Feist 2003). Whilst higher peak air change rates of 3 have been measured, generally result were below 1 with in fact almost no air change on calm summer days. The average air change range measured for these projects were in the range of Conclusions 3.1 PHPP Pre Assessment Results are summarised in the form of an analysis matrix included in Appendix A. Passivhaus Verification All three construction methods will result in Passivhaus compliant designs for space heating demand, primary energy demand and overheating when modelled with the current weather file. Passivhaus Verification Project specific figures Frequency of Overheating to be < 10% Specific Primary Energy Demand < 120 kwh/sqm/a Specific Space Heat Demand to be < 15 kwh/sqm/a Figure 1: Overheating, space heating demand and specific primary energy demand for the St Loyes Care home project when modelled using the Exeter current weather data. Space Heating Demand For central Europe (40 o - 60 o Northern latitudes), a dwelling is deemed to satisfy the space heating demand Passivhaus criteria if the total energy demand for space heating and cooling is less than 15 kwh/m 2 /yr treated floor area, the frequency of overheating is limited to a maximum of 10% and the specific primary energy demand is less than 120 kwh/m 2 /yr. For the St Loyes Care Home project the total energy demand for heating has been calculated as 8 kwh/m 2 /yr. 1 PH Requirements Overheating Dependant on the construction method the frequency of overheating has been calculated as 0-1%. However, this does not mean the building will not

8 Gale & Snowden Architects Ltd St Loyes Care Home PHPP Pre-Assessment Report Page 8 of 10 overheat under extreme weather conditions, and depending on user behaviour temperatures within the building may still exceed 25 degree Celsius. Specific Primary Energy Demand Whilst the calculated specific primary energy demand still fulfils the Passivhaus verification requirements it does not allow for any tolerance and any design change or change of the mechanical design strategy might cause the project to fail the Passivhaus target. The primary energy demand for a Passivhaus is typically in the region of 70kWh/m 2 /yr. The main factor detrimentally affecting the primary energy target for the St Loyes project is the direct electric heating. When applying the Passivhaus methodology to calculate the primary energy demand any electric energy used within a building is multiplied with the factor 2.58 to allow for transmission losses etc. To reduce the primary energy demand the heating strategy could be changed to a gas based system. The conversion factor for gas is 1.1 and would reduce the primary energy level by approximately kwh/m 2 /yr. Another alternative to reduce the primary energy demand would be to include solar panels. If sufficient allowance is made, about 50-60% of the hot water demand could be provided through solar energy and again reducing the primary energy demand by approximately kwh/m 2 /yr. 3.2 Overheating For a building to perform to Passivhaus standards an optimum summer comfort is equally as important as a reduced space heating demand and high thermal comfort in winter. The Passivhaus requirement limiting overheating in summer is expressed as the percentage of hours that the building is in use and where the internal temperature exceeds 25 degree Celsius. Based on empirical research by (Kolmetz 1996) summer comfort in residential buildings is still perceived as good if this figure stays below 10%. Whilst 10% is deemed acceptable, it is good practice to limit the frequency of overheating to below 5% and ideally 0% should be aimed for. Literature Review Research carried out by the PHI and others on built Passivhaus projects looking specifically at summer comfort have shown the following: Highly insulated, very air tight buildings like passive houses are able to maintain comfortable summer conditions without active cooling due to their increased thermal lag i.e. the ability to keep warm or cold for a longer period of time (PHI 1999). Because of this night cooling has proven especially successful in passive houses. The solar aperture of a building, achievable average summer ventilation rate and internal heat gains have a greater impact on internal summer climate than thermal mass (Feist 1998). This does not mean that thermal mass is not relevant. Both (Hauser 1997) and (Feist 1998) conclude that high levels of insulation whilst reducing the space heating demand in winter also protect from overheating in summer as long as adequate ventilation can be provided. (Average ventilation rates of that can readily be achieved with one tilted window per room will suffice.) When a building is insulated to Passivhaus standard with U values of <0.15 W/m²K solar gains through opaque building elements are negligible and will neither affect the space heating demand or internal summer temperatures. This is due to the thermal lag typically exceeding 12 hours and more (Feist 1998). PHPP Results for St Loyes The main findings with regards to overheating were as follows: 1. All three construction methods will result in Passivhaus compliant designs for overheating when modelled with the current weather file and without a requirement for additional shading. 2. The heavy weight construction without additional shading performs better in terms of overheating and will result in a lower daily temperature swing from solar gain than the light weight or medium weight approach. 3. Applying some form of shading and therefore controlling solar gains in summer has a far greater impact on reducing overheating in summer than thermal mass. This is true for all three construction methods. 4. When applying future weather files the frequency of overheating increases for all construction

9 Gale & Snowden Architects Ltd St Loyes Care Home PHPP Pre-Assessment Report Page 9 of 10 methods. In 2050 the building will require some form of solar control (e.g. shutters), in 2080 the building will be very close to failing the Passivhaus target of 10% independent from the construction method and additional measures to limit overheating will be required. 3.3 Space Heating Demand The PHPP modelling shows that the space heating demand is almost independent from the type of construction with regards to thermal mass. This is consistent with research carried out by (Feist 2000) that shows that the effect from thermal mass on the space heating demand of a well insulated building is less than 0.5%. Until 2030 the space heating demand remains constant and then decreases by 30% by 2080 due to expected rising average temperatures and a reduced annual heating season. These results are consistent with research carried out by the CIBSE. It could be argued that in the future super insulation and low energy design principles will be less important with the future UK climate becoming milder. However, at the same time fuels prices are expected to increase by 50% by 2050 (IEA 2009) and therefore net heating costs are likely to increase. Furthermore it has been shown (Feist 1998) that the same low energy design principles that reduce the heating demand in winter have proven to be successful in reducing the frequency of overheating in summer. However, for the St Loyes Care Home project the reduction in space heating demand might open up an opportunity to address overheating in 2050 and When the windows are due to be exchanged at the end of their useful life these could be exchanged for a glazing system that better controls solar gains to further reduce the risk of overheating and accepting the higher heat losses. If a glazing with a reduced g value (to BS EN 410) of 0.4 would be specified the frequency of overheating could be reduced by another 4%. The effect on the space heating demand under future climate conditions (2080) would be negligible. References (Feist 1998) (Feist 2000) (Feist 2003) Passivhaus summer climate Is insulating more effective than thermal mass Summer ventilation in passive houses (Hauser 1997) Impact of improved Uvalues on summer comfort levels (IEA 2009) 2009 Market Outlook International Energy Agency (Kolmetz 1996) Thermal analysis of buildings under summer conditions (Schnieders1999) Natural Night time Ventilation, Passivhaus Sommerfall (PHI 2007) PHPP Manual 2007

10 Gale & Snowden Architects Ltd St Loyes Care Home PHPP Pre-Assessment Report Page 10 of 10 Appendix A Results Matrix ) Item Description 1.1 Building as designed but without balconies on the south elevation Thermal mass Low Specific Space Heat Demand in kwh/sqm/a Current weather file 2030 weather file (a1fi/50percentile/try) 2050 weather file (a1fi/50percentile/try) 2080 weather file (a1fi/50percentile/try) Specific Primary Energy Demand kwh/sqm/a Frequency of Overheating % Medium Specific Space Heat Demand in kwh/sqm/a Specific Primary Energy Demand kwh/sqm/a Frequency of Overheating % High Specific Space Heat Demand in kwh/sqm/a Specific Primary Energy Demand kwh/sqm/a Frequency of Overheating % Building as designed including balconies on the south elevation Low Specific Space Heat Demand in kwh/sqm/a Specific Primary Energy Demand kwh/sqm/a Frequency of Overheating % Medium Specific Space Heat Demand in kwh/sqm/a Specific Primary Energy Demand kwh/sqm/a Frequency of Overheating % High Specific Space Heat Demand in kwh/sqm/a Specific Primary Energy Demand kwh/sqm/a Frequency of Overheating % Building including balconies on the south elevation and movable shutters fixed to balcony Low Specific Space Heat Demand in kwh/sqm/a Specific Primary Energy Demand kwh/sqm/a Frequency of Overheating % Medium Specific Space Heat Demand in kwh/sqm/a Specific Primary Energy Demand kwh/sqm/a Frequency of Overheating % High Specific Space Heat Demand in kwh/sqm/a Specific Primary Energy Demand kwh/sqm/a Frequency of Overheating % Building including balconies on the south elevation and movable shutters fixed to balcony with reduced g Value glazing system (g Value = 0.4) Low Specific Space Heat Demand in kwh/sqm/a 8 6 Specific Primary Energy Demand kwh/sqm/a Frequency of Overheating % Medium Specific Space Heat Demand in kwh/sqm/a 8 6 Specific Primary Energy Demand kwh/sqm/a Frequency of Overheating % High Specific Space Heat Demand in kwh/sqm/a 8 6 Specific Primary Energy Demand kwh/sqm/a Frequency of Overheating % 0 8