NZER (Nearly Zero Energy Retrofit ) -
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as PDF Low energy retrofit of a 4 bed 1978 chalet bungalow in West Sussex. Starting point for retrofit was EPC B, with double glazing, cavity wall insulation, goal was to make the house carbon negative in operation, even if not possible to make a completely zero carbon building (when considering both construction and operation).
NZER (Nearly Zero Energy Retrofit ) - : Project images
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Energy and fuel use
Renewable electricity generation This project has used the contributions from renewable electricity generation equipment to either meet the Retrofit for the Future target or otherwise reduce the Primary energy requirement and CO₂ emissions associated with the project.
Measured data from renewable generation is not yet available.
Fuel use
| Pre-development | Forecast | Measured | |
| Electricity use | 551 kWh/yr | 4000 kWh/yr | 3167 kWh/yr |
|---|---|---|---|
| Natural gas use | 23176 kWh/yr | - | - |
| Oil use | - | - | - |
| LPG use | - | - | - |
| Wood use | - | - | - |
| electricity sold to grid | -500 kWh/yr | -1000 kWh/yr | -1757 kWh/yr |
| Pre-development | Forecast | Measured | |
| Primary energy requirement | 155 kWh/m².yr | 43 kWh/m².yr | 20 kWh/m².yr |
|---|---|---|---|
| Annual CO₂ emissions | 28 kg CO₂/m².yr | 10 kg CO₂/m².yr | 5 kg CO₂/m².yr |
| Annual space heat demand | 100.5 kWh/m².yr | 27.5 kWh/m².yr | 21.9 kWh/m².yr |
Renewable energy
| Electricity generation | Forecast | Measured |
|---|---|---|
| Solar PV | 4000 kWh/yr | 3830 kWh/yr |
| Battery storage 10 kWh | - | - |
| Electricity consumed by generation | - | - |
| Primary energy requirement offset by renewable generation | -15 kWh/m².yr | -35 kWh/m².yr |
| Annual CO₂ emissions offset by renewable generation | -4 kg CO₂/m².yr | -8 kg CO₂/m².yr |
Calculation and targets
| Whole house energy calculation method | PHPP |
|---|---|
| Other whole house calculation method | - |
| Energy target | EnerPHit |
| Other energy targets | - |
| Forecast heating load | 16.2 W/m² demand |
Airtightness
| Date | Result | |
| Pre-development air permeability test | - | - |
|---|---|---|
| Final air permeability test | 22 April 2022 | 1.77m³/m².hr @ 50 Pascals |
Project description
| Stage | Occupied |
|---|---|
| Start date | 01 April 2021 |
| Occupation date | 15 October 2005 |
| Location | Hassocks West Sussex England |
| Build type | Refurbishment |
| Building sector | Private Residential |
| Property type | Detached |
| Construction type | Masonry Cavity |
| Other construction type | Cavity wall insulation + 200mm EPS EWI, rendered |
| Party wall construction | N/A |
| Floor area | 173 m² |
| Floor area calculation method | Treated Floor Area (PHPP) |
| Building certification |
Project Team
| Organisation | |
|---|---|
| Project lead person | Nick Owens |
| Landlord or Client | Nick Owens |
| Architect | Jim Miller Design Ltd |
| Mechanical & electrical consultant | Client |
| Energy consultant | Owens Insight Ltd |
| Structural engineer | De Silva Structures Limited |
| Quantity surveyor | None |
| Consultant | |
| Contractor | DP Johnston Ltd |
Design strategies
| Planned occupancy | 2 retired |
|---|---|
| Space heating strategy | Micro-CHP installed 2010,removed March 2021 and air source heat pump installed. |
| Water heating strategy | From heat pump with 170 litre thermal store for hot water. |
| Fuel strategy | Gas boiler with CHP till March 2021, all electricity thereafter with 4.4kW peak solar PV operational from Feb 2022. |
| Renewable energy strategy | Maximising available solar PV on south facing roof (street-side), whilst avoiding ugly facade. From 2015 have 7 PV panels @ 250w each, generating 1600kWh/year; added 6 panels of 450w each to give 4.45kW array generating ~ 4,000kWh/yr. |
| Passive Solar strategy | Increasing window sizes slightly on south facing facade; but limiting solar gain (and heat loss) by installation of predominantly triple glazing throughout. Built-in external blinds on south facing windows. |
| Space cooling strategy | Control overheating with: louvred external blinds on south facade; ability for night-time passive stack ventilation via 1 downstairs security-grilled window and rooflights in a north facing bedroom. Thermal mass in brick+block walls, in wood fibre insulation in barn-style roof and around dormers, is expected to control overheating. Floors on ground floor remain uninsulated concrete, though with EWI 400mm below DPC level. |
| Daylighting strategy | Modelled with DesignBuilder. Currently adequate in all living and bedrooms. |
| Ventilation strategy | House is on a windy ridge 58m above sea level, so ventilation is achieved by (1) MVHR; (2) open-able windows; (3) Passive stack strategy as described in space cooling above. |
| Airtightness strategy | Sought to achieve targeted air-tightness of 1 ach-1 from the roof replacement, EWI and internal airtightness measures. In event only reached 1.55 ach-1 because of large roof area and failure to specify airtight OSB. Effect on energy usage minimal. |
| Strategy for minimising thermal bridges | (1) Lapping EWI onto the window frames, (2) 400mm deep x 160mm thick XPS from DPC downwards to below ground level, (3) External not internal wall insulation, (4) warm roof with wood fibre insulation in eaves butted up against EWI. |
| Modelling strategy | Retrofit strategy developed by modelling the house both with DesignBuilder thermal simulation software and with PHPP version 9.6 both before retrofit and in developing the plan. |
| Insulation strategy | 200mm EPS EWI plus render on cavity-filled brick walls, with complete re-roof and re-tile to deliver 100mm wood-fibre insulation between rafters and 200mm above rafters. Dormer windows re-clad with 200mm wood fibre on cheeks and roof, with clay tiling rain screen |
| Other relevant retrofit strategies | Monitoring was undertaken before designing the retrofit, of internal temperature and relative humidity in 4 of the rooms plus external temperature, over a 3 month period. This data was used to baseline the gas and electricity energy consumption in the pre-retrofit DesignBuilder and PHPP models. |
| Contextual information | The environmental monitoring was undertaken as part of a dissertation for the University of Kent MSc in Architecture & the Sustainable Environment. The hypothesis the dissertation was testing is whether a 1970s chalet bungalow could economically be made zero carbon both in operation and construction (by use of carbon-sequestering wood fibre insulation + solar PV). The indicative result is yes as regards operation but no as regards construction, if end-of-life demolition is also taken into account; but in any event, not economically i.e. it did not save enough money to pay back over 50 years @ 2019 prices. Maybe does now post invasion of Ukraine. |
Building services
| Occupancy | 2 |
|---|---|
| Space heating | ASHP 30 - 40 deg.C (weather dependent) |
| Hot water | ASHP 50 deg.C |
| Ventilation | Zehnder MVHR |
| Controls | Radiator thermostats (mechanical, 15 yrs old); digital room thermostats (1) controlling room heating in hall and (2) controlling underfloor heating in kitchen/diner. |
| Cooking | Electric induction hob (max load 3kW) + oven + microwave + electric grill/small oven. |
| Lighting | Low energy lighting 95%of outlets. |
| Appliances | Dishwasher; tumble dryer; washing machine; kettle. |
| Renewable energy generation system | Solar PV |
| Strategy for minimising thermal bridges | As design |
Building construction
| Storeys | 2 |
|---|---|
| Volume | 485m³ |
| Thermal fabric area | 450 m² |
| Roof description | 100mm wood fibre insulation between rafters; osb board (not very airtight - wrong board specified); 200mm wood fibre insulation above rafters; Solitex membrane joints taped; Wood battens + counter-battens; Clay tiles. |
| Roof U-value | 0.15 W/m² K |
| Walls description | Cavity brick & block with 200mm EPS EWI plus render |
| Walls U-value | 0.13 W/m² K |
| Party walls description | N/A |
| Party walls U-value | - |
| Floor description | 1978 solid concrete, no extra insulation, variously covered with 12mm engineered oak flooring; under-floor heating array + 12mm engineered oak; or carpet. u-value below is an average. Next time would insulate concrete at very least with Slentex A2 aerotherm. |
| Floor U-value | 0.78 W/m² K |
| Glazed doors description | Triple |
| Glazed doors U-value | 0.78 W/m² K installed |
| Opaque doors description | |
| Opaque doors U-value | - - |
| Windows description | 90% are triple glazed. Those on south facing facade are triple glazed + exterior venetian blinds + 4th pane to keep these clean. Other 10%are remaining old oak frame double glazed windows. Windows u-value below is Uw installed av. including garage door. |
| Windows U-value | 0.99 W/m² K installed |
| Windows energy transmittance (G-value) | 61 % |
| Windows light transmittance | 53% |
| Rooflights description | Fakro |
| Rooflights light transmittance | - |
| Rooflights U-value | 0.51 W/m² K |