gale & snowden phpp pre-assessment report passivoffice

Swallow Court - PassivOffice@J27

PHPP Pre-Assessment Report

Gale & Snowden Architects & Engineers May 2012

Gale & Snowden Architects Swallow Court – PHPP Pre-Assessment Report of 11

Swallow Court - PassivOffice@J27

PHPP Pre-Assessment Report

Prepared by: Tomas Gärtner

Checked by: Maria Gale/David Gale

Project: St Loyes Care Home

Version: Final

Date: May 2012

Job No: B1113

Reference: Projects\Current\B1113 PassivOffice \Reports & Specs

Rev No Comments Date

This document has been produced by Gale & Snowden for the Swallow Court 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: 01237 474952 F: 01237 425449 www.ecodesign.co.uk Company No. 5632356 VAT Registration No. 655 9343 06


Executive Summary

This report illustrates the key findings of the PHPP pre assessment for the Swallow Court project modelled under current weather conditions and also future weather data provided by Exeter University’s Prometheus project.

Three different shading scenarios, two different construction methods and two ventilation options have been modelled. In addition ground cooling via an earth tube system has been assessed.

Main Findings

1. Both 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 only marginally better in terms of overheating but will result in a slightly lower daily temperature swing from solar gain than the medium weight approach. If the achievable average ventilation rate during summer can be increased by eg installing an oversized MVHR, then a heavy weight approach will outperform the intermediate weight solution.

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.

4. When applying future weather files the frequency of overheating increases for all construction methods. In 2050 the building will require some form of solar control (e.g. shutters) or change in ventilation strategy, in 2080 the building will fail the Passivhaus target of 10% independent from the construction method if no additional measures like for example ground cooling via a subsoil heat exchanger (SHX) is implemented.


Contents

Executive Summary ....................................................................................................................................................... 3

Contents ......................................................................................................................................................................... 4

1.0 Introduction .............................................................................................................................................................. 5

1.1 This Report ........................................................................................................................................................... 5

1.2 Thermal Assessment & Calculation ..................................................................................................................... 5

1.3 Heat Loss Methodology ....................................................................................................................................... 5

1.4 Building Fabric and Mechanical Design ............................................................................................................... 5

2.0 PHPP ....................................................................................................................................................................... 7

2.1 Passivhaus Standard ........................................................................................................................................... 7

2.2 Weather Files ....................................................................................................................................................... 7

2.3 Shading ................................................................................................................................................................ 7

2.4 Thermal Mass ...................................................................................................................................................... 7

2.5 Ventilation ............................................................................................................................................................ 7

3.0 Conclusions ............................................................................................................................................................. 8

3.1 PHPP Pre Assessment ........................................................................................................................................ 8

3.2 Overheating .......................................................................................................................................................... 9

3.3 Space Heating Demand ....................................................................................................................................... 9

References ................................................................................................................................................................... 10

Appendix A – Results Matrix ........................................................................................................................................ 11

Gale & Snowden Architects Ltd Swallow Court – PHPP Pre-Assessment Report of 11

1.0 Introduction

1.1 This Report

The purpose of this report is to illustrate the key findings of the PHPP pre assessment for the Swallow Court 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, ventilation 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


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 all high level windows tilted all night

Summer Day time ventilation Cross ventilation All windows tilted for 6hrs/day

Domestic Hot Water

• TBC

• Flow and return distribution with 24h circulation

• 25mm air based insulation to pipes

• Solar hot water

Space Heating

• TBC

Electricity Demand

An allowance has been made for 50 office work spaces and one fully fitted kitchen. The following equipment has been allowed for:

50 No PC @ 80W

50 No Screens @ 28W

4 No Telephone system @ 100W

4 Copy machines @ 400W

10 Printer @ 300W

Fitted kitchen including electric cooker, microwave, dishwasher, fridge and kettle.

Lighting

The energy demand for lighting is calculated on the basis of the required luminance and achievable daylight levels. For this the average daylight level is calculated on the basis of the proposed design, detailing and window specification. The results are then used to identify the probability of using artificial lighting throughout the year.

The following light levels have been allowed for

Offices 500 Lux (equiv. to 15W/sqm)

Kitchen 300 Lux (equiv. to 9W/sqm)

Circulation/WC 200Lux (equiv. to 7W/sqm)

Internal Heat Gains

The PHPP allows for two alternative methods to identify internal heat gains.

For the verification of the total heating demand a fixed value of 3.5W/sqm treated floor area was allowed for. This figure is to be used for showing compliance with the Passivhaus standard.

Alternatively the PHPP allows to calculate internal heat gains based on the actual energy use within the building and the heat given off by people depending on their age group and activity, also taking into account actual utilisation patterns for the building based on the clients brief.

Based on the age group and level of activity 100W per person has been allowed for.

According to the client’s brief the building will be in use during typical office hours ie 8am-6pm.

Internal heat gains from lighting, equipment, hot water systems is based on the actual average energy demand calculated in the PHPP.

For the Swallow Court project average internal heat gains of 5.2 W/sqm have been calculated.

For the calculation of the frequency of overheating 5.2W/sqm was used in the PHPP. Because it exceeds the standard value it can be seen as the worst case scenario.

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




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, two different construction methods and two ventilation options have been modelled. In addition ground cooling via an earth tube system has been assessed.

The building has been modelled with shading provided only by roof overhangs and window reveals, with additional shading provided by flexible external blinds to the SW/SE facing elevation and flexible external shading to all windows.

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 as the storage mass accessible from the room is increased.

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.

For this project an intermediate weight construction has been modelled as the base case. A heavy weight approach has been assessed as an alternative to assess its potential of reducing overheating.

2.5 Ventilation

For the base case 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 high level 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 0.6 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 0.5-0.8.

As an alternative an oversized MVHR system that is capable of providing 1 ach was allowed which would operate in summer bypass mode to assist the natural ventilation strategy.

As a third alternative a subsoil heat exchanger has been allowed for. This system would consist of a 200mm diameter PE pipe buried in the ground around the building at foundation level and connected to the fresh air intake of the MVHR. Because the ground remains at a more or less even temperature of ~10 degree C throughout the year the fresh air would be pre-cooled in summer and pre-heated in winter before it enters the MVHR.

3.0 Conclusions

3.1 PHPP Pre Assessment

Results are summarised in the form of an analysis matrix included in Appendix A.

Passivhaus Verification

Both construction methods (heavy weight and intermediate weight) will result in Passivhaus compliant designs for space heating demand, primary energy demand and overheating when modelled with the current weather file.

Figure 1: Overheating, space heating demand and specific primary energy demand for the Swallow Court project when modelled using the Exeter current weather data.

Space Heating Demand

For central Europe (40o - 60o 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/m2/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/m2/yr.

For the PassivOffice project the total energy demand for heating has been calculated as 5 kWh/m2/yr.

Overheating

Dependant on the construction method the frequency of overheating has been calculated as 0-1% when using current weather data. However, this does not mean the building will not overheat under extreme weather conditions. Depending on user behaviour (ie eg if the windows are opened as assumed here) 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 main factor detrimentally affecting the primary energy target for the Swallow Court project is the direct electric heating and hot water system.

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 biomass based system. The conversion factor for wood is 0.2 and would reduce the primary energy level by approximately 10-15 kWh/m2/yr.

5

118

0

Specific Space Heat Demand to be < 15

kWh/sqm/a

Specific Primary Energy Demand < 120 kWh/sqm/a

Frequency of Overheating to be < 10%

Passivhaus VerificationProject specific figures PH Requirements


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 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 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 0.5-0.8 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 Swallow Court

The main findings with regards to overheating were as follows:

5. Both construction methods will result in Passivhaus compliant designs for overheating when modelled with the current weather file and without a requirement for additional shading.

6. The heavy weight construction without additional shading performs only marginally better in terms of overheating but will result in a slightly lower daily temperature swing from solar gain than the medium weight approach. If the achievable average ventilation rate during summer can be increased by eg installing an oversized MVHR, them a heavy weight approach will noticeably outperform the intermediate weight solution.

7. 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.

8. When applying future weather files the frequency of overheating increases for all construction methods. In 2050 the building will require some form of solar control (e.g. shutters) or change in ventilation strategy, in 2080 the building will fail the Passivhaus target of 10% independent from the construction method if no additional measures like for example ground cooling via a subsoil heat exchanger (SHX) is implemented.

3.3 Space Heating Demand

The space heating demand shown in appendix A is considerably lower than the 5kWh calculated for Passivhaus compliance because higher internal gains (based on actual calculations rather than standard values) have been assumed for the overheating analysis.

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% 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 fuel 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.

References

(Feist 1998) ‘Passivhaus summer climate’

(Feist 2000) Is insulating more effective than thermal mass?

(Feist 2003) 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


Appendix A – Results Matrix

E0810 Swallow Court Rev n/a

Overheating Analysis Work Stage E29/03/2011

2004 2030 2050 2080Construction: Intermediate weight construction ie 50% of space enclosing elements are of heavy weight construction

Frequency of Overheating (%) 0 9 16 33

Summer Ventilation: naturally ventilated via windows; tilted high level windows for night cooling

Heating Demand (kWh/sqm/yr) 2 1 1 1

Shading: partly shaded via roof overhangsPrimary Energy Demand (kWh/sqm/yr) 119 119 118 117

Construction: Heavy weight construction ie 100% of space enclosing elements are of heavy weight construction


Summer Ventilation: naturally ventilated via windows; tilted high level windows for Heating Demand (kWh/sqm/yr) 2 1 1 1

1

2

Current Design (Base Case)

Current design with Heavy weight construction

via windows; tilted high level windows for night cooling



Construction: Intermediate weight construction ie 50% of space enclosing elements are of heavy weight construction


Summer Ventilation: MVHR in summer bypass mode; naturally ventilated via windows; tilted high level windows for night cooling





Summer Ventilation: MVHR with SHX (for ground cooling) in summer bypass mode; naturally ventilated via windows; MVHR for



3

4 Current design with Oversized MVHR (1.0 ach) in summer bypass mode to assist natural ventilation strategy

Current design with MVHR in summer bypass mode to assist natural ventilation strategy

Primary Energy Demand (kWh/sqm/yr) 119 119 119 118





Shading: External shading to roof lights and SW/SE facing windows Primary Energy Demand (kWh/sqm/yr) 119 119 119 118





Shading: Flexible external shading to all roof lights and windows Primary Energy Demand (kWh/sqm/yr) 119 119 119 118

Construction: Heavy weight construction ie 8

5

6 Current design with Flexible external shading to all roof lights and windows

High mass construction plus

Current design with Flexible external shading to roof lights and SW/SE facing windows

100% of space enclosing elements are of heavy weight construction


Summer Ventilation: MVHR in summer bypass mode; naturally ventilated via windows; tilted high level windows for night cooling





Summer Ventilation: MVHR with SHX (for ground cooling) in summer bypass mode; naturally ventilated via windows; MVHR for night cooling





Summer Ventilation: MVHR in summer bypass mode; naturally ventilated via Heating Demand (kWh/sqm/yr) 2 1 1 1

9

10

High Mass plus Oversized MVHR (1.0 ach) in summer bypass mode to assist natural ventilation strategy

Current design with MVHR (standard rate) in summer bypass plus flexible external shading to all roof lights and windows

g pMVHR (standard rate) in summer bypass mode to assist natural ventilation strategy

bypass mode; naturally ventilated via windows; tilted high level windows for


Shading: Flexible external shading to all roof lights and windows Primary Energy Demand (kWh/sqm/yr) 119 119 119 118

windows



Summer Ventilation: MVHR with SHX (for ground cooling) in summer bypass mode; naturally ventilated via windows; tilted high level windows for night cooling



Construction: High mass construction ie 100% of space enclosing elements are of heavy weight construction


Summer Ventilation: MVHR with SHX (for ground cooling) in summer bypass mode; naturally ventilated via windows; tilted high level windows for night cooling



Construction: Intermediate weight

12

13

11

Current design with High mass plus Use of MVHR combined with a Subsoil Heat Exchanger (ground cooling) in summer bypass mode to assist natural ventilation strategy

C rrent design ith O ersi ed

Current design with MVHR (standard rate) combined with a Subsoil Heat Exchanger (ground cooling) in summer bypass mode to assist natural ventilation strategy



Summer Ventilation: MVHR with SHX (for ground cooling) in summer bypass mode; naturally ventilated via windows; MVHR for night cooling



13 Current design with Oversized MVHR (1.0 ach) combined with a Subsoil Heat Exchanger (ground cooling) in summer bypass mode to assist natural ventilation strategy

30

35

Current Design (Base Case)

Current Design with Heavy weight construction

15

20

25

Current Design with MVHR in summer bypass mode to assist natural ventilation strategy

Current Design with Oversized MVHR (1.0 ach) in summer bypass mode to assist natural ventilation strategy

Current Design with Flexible external shading to roof lights and SW/SE facing windows

Current Design with Flexible external shading to all roof lights and windows

Current Design with High mass construction plus MVHR (standard rate) in summer bypass mode to assist natural ventilation strategy

5

10

Current Design with High Mass plus Oversized MVHR (1.0 ach) in summer bypass mode to assist natural ventilation strategy

Current Design with MVHR (standard rate) in summer bypass plus flexible external shading to all roof lights and windows

Current Design with MVHR (standard rate) combined with a Subsoil Heat Exchanger (ground cooling) in summer bypass mode to assist natural ventilation strategy

Current Design with High mass plus Use of MVHR combined with a Subsoil Heat Exchanger (ground cooling) in summer bypass mode to assist natural ventilation strategy

Current Design with Oversized MVHR (1.0 ach) combined with a Subsoil Heat Exchanger (ground cooling) in summer bypass mode to assist natural ventilation strategy

0

2004 2030 2050 2080

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