| Planned occupancy | The house is occupied by a married couple and their grown up daughter. It is expected that they will remain in occupation throughout the retrofit work and the project has been designed to make this possible. |
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| Space heating strategy | High efficiency ground source heat pump serving low temperature (45/40oC) high thermal mass two-pipe radiators. Control by progammable timeclock and zone thermostat. TRVs on bedrooms and kitchen only. |
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| Water heating strategy | High efficiency ground source heat pump serving primaries of indirect mains pressure factory insulated hot water cylinder. Timeclock controlled charging periods and storage temperature thermostat set point at 60oC. Electric immersion heater fitted for emergency use only. |
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| Fuel strategy | This project uses mains electricity as its main fuel with some further electricity from a PV system. Key drivers for the use of electricity are the absence of main gas in this rural location and the cost and carbon consequences of the fossil fuel alternatives oil and coal. Penwith HA has previously demonstrated in its pioneering work with ground source heat pumps that they can provide very cost effective space and water heating with very low CO2 emissions in off gas areas. |
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| Renewable energy strategy | Despite objections from some purists it is now widely accepted (including by government agencies) that ground source heat pumps are renewable energy systems. The key renewable component is the solar energy retrieved from the ground by the ground loop. The key feature of this project is it's innovative ground / air / solar source heat pump which achieves a 25% improvement on the performance of traditional GSHPs. The design also includes a 0.25kWp PV array for direct coupling to 12v DC fans and pumps only. |
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| Passive Solar strategy | HeatPod solar porch tempers incoming fresh air supply for mech. vent system. Balancing mechanical extract recovers solar gain using coil in low temp. ground loop circuit to supplement stored solar energy in ground . |
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| Space cooling strategy | Mechanical vent system can be boosted to increase summer time flow rate, otherwise windows are openable. |
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| Daylighting strategy | This project does not propose to alter the existing house in this respect. It is planned to replace the existing windows with new triple glazed high performance units, but these will retain patterns similar to the existing windows to avoid radical change in the appearance of the property. Owing to the relatively small size of the house it is well served by traditional windows for daylighting purposes. |
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| Ventilation strategy | Controlled balanced supply and extract provides fresh air ventilation . |
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| Airtightness strategy | The project includes provision for a programme of pre and post retrofit pressure testing. From past experience of pressure testing Penwith HA properties of this era it has been found that their air tightness is better than might be expected owing to the original use of render and plaster finishes to concrete floors and block walls. The retrofit's inclusion of external wall insulation and high performance windows and doors (and careful sealing of the joints between these elements) is expected to significantly improve air tightness of the main envelope. It is intended to enhance air tightness between walls and first floor ceilings by the addition of sealed coving. There will then be further joint sealing carried out to any areas of weakness revealed by the first post-retrofit pressure test. By these means it is planned to reduce uncontrolled ventilation losses to 3 ACPH. |
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| Strategy for minimising thermal bridges | There are three main areas of weakness in terms of thermal bridging: Window and door openings, the solid concrete ground floor and the Finlock gutters. (These consist of a pre-cast concrete cavity closer with an integral concrete gutter. They were widely used in the 1950s). In the retrofit the window and door opening detail will be changed so that window & door frames span the junction between the external insulation and external wall, eliminating cold bridging at that point. To reduce heat losses from the ground floor the external wall insulation will extend 600mm below dpc level. The thermal bridging at the Finlock gutters will be overcome by fixing a layer of insulation board with a coving internally at first floor ceiling level. With careful detailing and matching decorations this will not be intrusive and will avoid radical alteration of the Finlock gutters. |
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| Modelling strategy | Load and energy modelling carried out by NHER/SAP2005 and SAP Extension plus various load duration analysis techniques (ESIBEEP and EN15316-2-4:2008) to deliver full multiple source energy matching as well as the monthly energy summaries necessary for any standard gshp design. |
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| Insulation strategy | Penwith HA has very substantial practical experience of external wall insulation which has been used very effectively on approximately 1000 houses in its stock over a 25 year period. It is very effective in enclosing the thermal mass of a dwelling, tempering the fluctuation of internal temperatures, and when used with replacement windows and doors it significantly reduces air leakage. The innovations here are in applying external insulation to a previously cavity filled wall, doubling the traditional thickness of insulation and use of the system below ground to reduce heat losses from the solid ground floor. The system will include 100mm thick phenolic board external wall and ground floor edge insulation. The wall insulation will be complimented by high performance triple glazed windows and doors. This package will be completed with 400mm loft insulation and air pressure testing and and sealing areas of uncontrolled ventilation. |
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| Other relevant retrofit strategies | It is an important feature of this project that it is designed to be applied to an occupied dwelling. It builds on Penwith HAs long experience of refurbishing and retrofitting existing homes and the knowledge that most tenants can cope with work to the outside of their home. Hence the external wall insulation, window & door replacement and the design of the HeatPod placing M&E equipment outside the dwelling. Although there will be internal work, it is kept to a minimum. This approach presents a much more achievable retrofit for large scale roll out than designs which require substantial internal alteration. |
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| Contextual information | This project is located in rural Cornwall only a few miles from Lands End, the most Westerly point in England. Despite being in an area of outstanding natural beauty, low incomes, unemployment and fuel poverty are common. The site of this project, in common with much of Penwith, does not have mains gas and can experience very severe weather in winter. The retrofit solution for this project, whilst entirely appropriate for replication in less demanding areas, is particularly suited to this type of environment. |
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