Feeling the benefits of saving energy

14 03 2012

We’re quite proud of this article that we knew nothing about until we read it in the local paper in March 🙂





HHP Retrofit for the Future project – one year on …

8 03 2012

The two houses in Newark that we retrofitted in 2010 as part of the Technology Strategy Board’s Retrofit for the Future project have now been re-occupied for over 12 months.  As part of the project, the energy use and environmental conditions are being monitored for 2 years following the retrofit, so we’ve done some initial analysis of the first year’s data, and here’s a summary of our findings.

In one house, the tenants are the same retired couple that lived in the house prior to retrofit, so we can compare the past year’s consumption with previous bills as well as the post-retrofit predicted energy use from the SAP calculations.

Prior to the retrofit, the couple’s annual energy use was 15,695kWh.  For the first 12 months of occupation post retrofit, Oct 2010 to Oct 2011, their total energy use was 5,305kWh, a reduction of 66.2%.  As a part of the retrofit solution, we decided to make an investment in a local community-owned wind turbine, rather than install renewables on the houses (as this was not appropriate for a number of reasons).  Including one house’s share of the annual production of the wind turbine, 1,943kWh, means a net consumption for this house of 3,362kWh, a reduction of 78.6%.

The reduction in annual CO2 emissions is lower at 57.9% due to the fact that all energy use in the house is now electricity, which has higher carbon intensity than gas.

Electricity is also more expensive per kWh than gas, so the reduction in annual fuel bills is also lower at 26.4%, but we have to remember that this is in a climate of rising energy prices, where other consumers would have probably seen their bills rise by an average of 10-15% in the same time period, so in real terms the residents have seen a reduction in energy costs of 35-40%.

The post retrofit SAP calculations predicted an annual energy use of 4,385kWh, but this is only for heating, hot water, ventilation and lighting energy use.  We are monitoring 8 individual electrical sub-circuits in the houses, so can compare SAP regulated energy predictions to actual usage.  This shows that actual energy use for these regulated elements was only 2,309kWh, 47% less than predicted.  Looking at the actual energy use for the sub-elements of the SAP calculation, heating and ventilation energy use were very similar to SAP predictions.  The largest reductions were energy for water heating, actual use of 1,186kWh compared to a SAP prediction of 2,696kWh, and lighting, actual use of 62kWh compared to a SAP prediction of 752kWh.  The residents clearly use lighting very sparingly!   In relation to the hot water disparity, this can probably be explained by the more efficient, HHP designed ‘Hotsi’ hot water system installed, and the fact that SAP assumes a greater occupancy for a property of this size – 2.53 occupants whereas there are only 2.

Analysing the breakdown further, non-regulated energy use (cooking and appliances), which is highly influenced by occupancy levels, accounts for 57% of the total energy use.  If we also include energy used for water heating, another element highly influenced by occupancy levels, then this percentage increases to 79%, which clearly illustrates the impact occupancy has on energy use in a very energy efficient house.

Annual gas consumption prior to the retrofit was 12,493kWh, which would have been primarily for heating and hot water, aside from a small amount of gas used for the hob.  Post retrofit, annual energy use for heating and hot water was 2,061kWh, an 83.5% reduction.

The neighbouring house that was retrofitted as part of the project is occupied by a couple with 4 children (which rose to 5 during 2011 – congratulations!)  However, they were not the pre retrofit occupants, so we cannot do a pre and post retrofit comparison of their energy use.  Their total energy use for their first year of occupation was 8,522kWh, or net of 6,579kWh after accounting for their house’s share in the community wind turbine.  This is almost double that of their neighbours, but there are 6 (now 7) occupants as opposed to 2 next door, and as we’ve seen occupancy has a significant influence on total energy use.

This analysis is based on the first year of occupancy, to Oct 2011, and there are a number of factors that we believe will have caused this 12-month period to have higher energy use than we’d otherwise expect:

  1. The retrofit design is based on the principals of passive solar design and high thermal mass (like the homes at HHP), but the houses were completed and re-occupied entering the heating season, so were still drying out and had not had chance to build up a store of energy in the mass to help them through the winter;
  2. The Envirovent MVHR units broke down and/or were replaced on numerous occasions during the first winter (the first house had 4 units in 12 months) leading to significant periods where the occupants had to open windows to ventilate the house, which completely undermines the design and will negatively impact thermal performance and the homes’ comfort;
  3. The winter of ’10-’11 was extremely harsh.

In relation to point 1, when the first house was re-visited in October 2011, the internal temperature was 24oC on a Sunday evening, and the occupants had not had to start using the electric heaters, whereas 12 months earlier when they first moved in the internal temperature was 19oC and the heaters were already on for a few hours each day.

As we exit the ‘11/’12 winter (hopefully!), which was much milder than the previous year, it looks like energy use is reducing, at least in the first house where occupancy levels are the same.  Comparing total energy use in this house for the November – February period with the same period from the previous year, shows a further 25.7% reduction.  In the second house, the energy use for the same period compared to the previous year has actually increased by 9.7%, but there is increased occupancy, and as we have seen, and see here at HHP, occupancy level has a significant impact on energy use in very energy efficient homes.

But what do the residents think about their new homes?  We’ve not been able to contact the family in the second home, but have spoken to the retired couple.  They had occupied the house for 40 years prior to the retrofit, so are well placed to comment on their new home.  There have been some issues, most notably the Envirovent MVHR units frequently failing in the first year, and occasionally find the house too hot in summer or too cold in winter, but on the whole they are very happy with their new home.





Early feedback on energy consumption

19 10 2010

The tenants of one house have now been back in their home for 2 weeks, and we’ve taken a look at their energy use over that period.

Their total energy consumption is averaging at 11.93kWh/day.  At that rate, their annual consumption will be 4,356kWh.  However, the heaters are on at the moment – averaging 2.27kWh/day (pretty low!) – so we’re hoping the annual use will be lower than this, as these will not be on all year.  It will also probably require more heating this winter as the house has been a building site for 6 months, and not able to build up a store of solar energy from the summer.

So how does this compare to their previous energy use?  Well, looking at 18 months of bills prior to the retrofit, they were averaging 3,241kWh/yr of electricity and 18,972kWh/yr of gas.

So down from an annual energy consumption of 22,213kWh to 4,356kWh – not a bad start; long may it continue …





Before and after photos

19 10 2010





Retrofit complete! Now for the monitoring

8 10 2010

We have now completed the retrofit of the houses, and hopefully you’ll agree they’re looking great.

Front of the completed properties

The rear of the completed properties

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.

Meters, meters and more meters!

We hope you’ve enjoyed our blog so far, and watch this space for more news of post occupancy evaluation …





The loft space and hot water

15 09 2010

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.

Significant levels of insulation in the loft

Although there is no access to the loft, the houses now additional storage areas in the sun space and porch.

Insulated thermal store

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.

Super insulated thermal store - it is in there, honest!





Heating and ventilation strategy

31 08 2010

The majority of the heating demand for the house is expected to be provided from three sources:

  1. 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;
  2. 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;
  3. 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.

Programmable timer and thermostat on one of the radiators

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 in the bathroom, which contains the fans and heat exchanger

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.