We have now completed the retrofit of the houses, and hopefully you’ll agree they’re looking great.
The existing tenants of number 30, Mr & Mrs Morton, have already moved back in and are enjoying their new home. Newark and Sherwood Homes are advertising for tenants for number 28, which was previously void.
The houses will now be monitored for 2 years to see how they really perform. The monitoring includes:
- Temperature and relative humidity in 3 rooms of the house (sitting room, bedroom 1 & bedroom 2)
- External temperature
- CO2 level in the sitting room
- Total water and electricity consumption
- Electricity consumption on 8 individual sub-circuits
All this data is being monitored automatically and transmitted to a central database at 5 minute intervals, and we can view it real-time via a website.
We are also hoping to do additional monitoring on the properties, and are in discussion with a couple of universities about the possibiliity of collaborating on this.
We hope you’ve enjoyed our blog so far, and watch this space for more news of post occupancy evaluation …
The generally recommeded level of loft insulation, and that provided in most new build houses today, is 250-300mm. The houses already had about 250mm of insulation in the loft, but we have topped that up to between 600-700mm. In addition, we have then sealed the loft hatch so that occupants cannot then compact the insulation by storing lots of belongings on top of it; if loft insulation is compacted, a lot of the benefit of the insulation is lost – it restricts heat transfer because of the air pockets within the fibres.
Although there is no access to the loft, the houses now additional storage areas in the sun space and porch.
The hot water in the houses is provided by a super-insulated thermal store heated with an electric immersion heater. A thermal store is like a traditional hot water cylinder, but the key difference is that the hot water in the cylinder is not the hot water used, instead it simply acts as a heat storage mechanism, hence the term thermal store. The hot water delivered to taps and showers, is actually cold water directly from the mains supply, which is then passed through a large copper coil (heat exchanger) within the thermal store, and in doing so extracts energy from the hot water in the store to heat it. As the water in the cylinder is not being used directly, it does not need to be heated to 60 degrees to kill legionella bacteria; instead it can be kept at aorund 45 degrees, significantly reducing energy consumption. The hot water delivered is around 40 degrees, more than adequate for washing and showering.
The majority of the heating demand for the house is expected to be provided from three sources:
- Passive solar gain, both directly into the house and harvested from the sun space, which will be absorbed and stored in the mass of the walls and floor, being released as the air temperature falls;
- Incidental gains from cooking, hot water and appliance use – these all produce heat as a by-product that will help to heat the house, again by being absorbed and stored in the mass of the walls and floor;
- Metabolic gains from occupancy – we all give off body heat, the amount varying depending on what activity is being undertaken, but again this heat will be absorbed and stored in the mass.
We have however made provision for top-up heating in the properties via provision of electric radiators in the sitting room and dining room, and electric towel rails in the bathrooms. If the house performs as expected though, these will require very little use.
The heaters are on a separate electrical circuit which is being monitored, so we will be able to see exactly how much top-up heat has been provided by the electric heating.
The houses are now hopefully very airtight – the actual level of airtightness achieved from the retrofit will be tested in the autumn and compared to the value beforehand – and as the design principles dictate not opening windows during winter, to minimise heat loss, then there needs to be provision for a fresh air supply, and extract of moisture from the kitchen and bathrooms.
We have therefore installed a mechanical ventilation with heat recovery unit, or MVHR for short. These devices use fans to extract the warm, moist air from kitchens and bathrooms, to prevent the build up of condensation and potential mould growth, and at the same time bring fresh air in to other rooms from outside. Both these air streams, the outgoing warm, moist air, and the incoming cooler, dry air, then pass through a heat exchange unit in which the latent heat in the air being extracted helps to pre-heat the cooler air being brought in from outside. The units we have installed have a heat recovery efficiency of 90%, i.e. 90% of the heat in the air being extracted is recovered to pre-heat the cooler air being brought in, so overall heat loss from the house is minimised.
The MVHR unit has one additional smart feature that will help to keep the house warm. We have worked with the manufacturers, EnviroVent, to modify the unit’s control logic and ducting, to optionally take air directly from the sun space when the house is cooler than a preset temperature, and the sun space is warmer than the house; this is effectively automating the harvesting of passive solar energy from the sun space, so the occupant doesn’t have to worry about opening doors to do this manually.
The windows and doors have now been fitted to the properties.
All the glazing on the house, including that into the porch and sun space, is triple glazed, krypton filled and with a low-emissivity coating; this makes the windows very energy efficient, with a U-value of 0.8 – the lower the U-value, the less heat is lost. The average U-value for double glazing is around 2.
The glazing on the sun space is double glazed; this doesn’t need to be as energy efficient as the glazing on the house itself, as the house and sun space are thermally separated with the triple glazed units. The sun space however is still well insulated, probably as well insulated as most new housing being built today, so will still retain heat reasonably well. As it is also sheltering a reasonable area of the rear of the house, it will help to further reduce heat loss from that area of the house fabric.