On the 10th March, DECC made an announcement about the much anticipated Renewable Heat Incentive.  Whilst many installers have expressed their disappointment, we welcome the approach being taken for domestic properties - the general approach being to delay actual tariffs until there is a greater understanding of the benefits, whilst offering a small grant to those willing to feed back about the actual benefits and performance of installations.

The Renewable Heat Incentive can be broadly split into three categories - biomass, heat pumps and solar thermal.  Each of these has come under scrutiny over the past few years and each seems not to be the panacea that they are oft touted as being.  There is a time and place for each but not every time and every place.

Solar Thermal
It seems generally the case that hot water occupies a great percentage of our consciousness than our actual energy bills - mainly because we are in much more direct contact with it than our radiators ticking away in the background. A way of thinking about the relative proportions of hot water to heat is to envisage spreading a nice hot bath of water throughout all my radiators - I don't think it would heat a normal house up much!

There are often very effective and much cheaper options for reducing hot water use  - combi boilers, improved tank and pipe insulation, low flow showerheads and shorter showers (and sharing baths :-) ).  This is why we analyse all these alongside solar hot water in our Masterplans.

A normal hot water bill will be around £150 - £250 a year, which can be reduced to around £100 - £175 with some low cost measures.  A solar thermal system might only save you up to 50% of this.  Instead a similar spend on walls could save you hundreds.

Heat Pumps
There are two types - air source and ground source.  They both work by using some electricity to turn the low grade heat in the ground or air into high grade heat in your house - essentially a fridge inside out.  Ground source are more efficient but require more space for underground pipework.

There are a number of questions and problems that need to be taken into account when looking at heat pumps -

1. They have large capital costs which makes then unaffordable to most people
2. Ground source require lots of space, which is only available to those with large plots
3. Air source are as noisy as a conversation
4. They can often lead to higher running costs depending on the heating system being replaced -  a major problem if the recipient of any RHI payments is different to the person paying the bills - e.g. in a social housing situation.
5. The actual efficiencies (Coefficients of Performance) are not well tested and where they have been tested are often be lower than published (see the results of a recent extensive Field Trial carried out by the Energy Saving Trust).
6. They are least efficient when the temperature differences between inside and outside are greatest - i.e. the middle of winter
7. Their associated carbon emission are dependent on the grid which has tended to become more carbon intensive over the past several years.

Biomass
The AECB recently published a paper (Biomass - a burning issue) outlining why Biomass was not always the best option.  Here is one of the opening statements:

"The use of biomass as a 'low or zero carbon fuel' is increasingly being adopted as the default solution to meet emission targets for new buildings.  This approach is fundamentally misguided and is leading to increased UK carbon emissions"

It seems things are not as simple as they seem and any scheme should take into account all the complication and issues raised in this paper.  There are also many of the same problems with costs and land as with heat pumps.

We strongly believe in the support and adoption of measures that will both reduce our CO2 emissions and reduce our dependence on fossil fuels. We also realise that there is limited resources available. The Governement's approach seems sensible to us, both to make sure that our limited resources are not used for less effective measures and also to ensure that the move to a lower Carbon Dioxide economy is not taken by those who can afford the capital costs, and borne by those who can least afford it.

If Green Deal advice (or any other for that matter) is based on 'standard usages' of properties, it may be extremely inaccurate.  In this posting we have taken a real property that we have surveyed, then amended the heating, hot water and electrical behaviour in various ways to see what the effect on difference upgrades would be....all modelling was done using our own home energy software.

A lot of housing energy analysis is performed on properties with 'standard usages'.  That's all well and good for benchmarking or extrapolating but can lead to inaccurate advice when applied to real houses and real people.

The two key questions are:
a) do behavioural differences really have significant effect on the energy use of a property and hence what we would advise to do with them and;
b) are standard usages (e.g. as per BREDEM, SAP, RdSAP) reflective of average usages?

Our experiences says that for a)  the answer is a categorical YES and for b) we don't know if they reflect an average of all people but our clients have certainly deviated from the 'standard usages' significantly and regularly.

The house
We took a standard 2 bed semi detached late Victorian property with 2 residents.  The gas boiler was about 78% efficient, the walls solid and the actual electrical use a little below national average.  The residents mainly showered using a standard shower.

Heating
The first thing we looked at was altering the residents' heating patterns. We predicted their annual total energy use using our model as 20,868kWh which was actually within 5% of their latest annual use based on meter readings.

We then altered the heat settings to reflect BREDEM standard daytime and weekend on/off times and temperatures, and also a high use scenario and a low use scenario.  The graph below shows the large differences in annual kWh predictions.

What we did next was to apply two seperate measures to each of the above four scenarios - a boiler upgrade and 50mm of PIR insulation onto the solid walls.  We then also looked at carrying out both a boiler upgrade and the internal wall insulation together as a package.  The total cost of the two measures has been set at £5,000 (£1,500 for the boiler and £3,500 for the IWI).  The figures show that the paybacks will range from around 4.5 years to 12 years depending on the different behavioural use.  More importantly the client may have thought they were going to save around £776 if they had been modelled against 'standard usages' but actually will only save £443 a year - the consequences for people taking out financing are obvious.

Hot Water Use
Heating isn't the only thing that varies with behavioural use.  We have looked at differences in hot water use too. Although not as dramatic, we hope the figures show that actual use of hot water is also important.  The range after tweaking behaviour but without changing the number of people in the house or how frequently they wash changes from 2681kWh to 3625kWh annually. That's a rise of 35% !

We applied two different measures to each of these scenarios.  A simple one which upgraded the showerhead and the the upgrading the boiler.  The most obvious aspect here is that the showerhead measure has no affect on the base case as only baths are taken.  It's obvious, but it does highlight the importance of differences between actual use and 'assumed use' quite bluntly.

Electricity Use
Finally we looked at the same house with just two different lighting use intensities. The actual use is not excessive so we compared that to a situation where they left the lights on more.  For simplicity we didn't change any appliances modelled usages.

As expected, the results show us that the expected savings are much greater when the lights are used a lot more.  The key point again is the actual savings would not be known when the actual usage is not taken into account.  When you are spending £15-£20 on an LED lamp knowing that the kitchen ones will payback in 2.5 years and the loft room in 25 years is important.

One of the proposed models for the Green Deal has been to evaluate energy savings based on individual measures installed. In this posting we've presented a worked example calculation showing the importance of evaluating installed energy saving measures as packages in evaluating savings and paybacks e.g. for the Green Deal.

When we look at all the options for a property we first of all evaluate the individual effects that each will have if carried out on their own.  Importantly we then use our judgement to build packages or suites of complementary measures to understand the net effect of them on the energy consumption and CO2 emissions.

To begin with we looked at 6 things that were possible for the house using our domestic energy modeling software (3 bed end of terrace Victoria solid wall....again).  This isn't an exhaustive list obviously.  The modelled energy cost of the house is £1,766 a year - its a pretty inefficient house.
 
The measures evaluatded were:

1. Upgrading the boiler from one with a permanent pilot light to a top specification boiler - install cost ~ £2,000
   
2. Installing 300mm of mineral wool loft insulation - install cost ~ £300
3. Internally insulating the solid external walls with 50mm of PIR insulation - install cost ~ £4,000
4. Zoning the house using thermostatic radiator valves to keep upstairs 2 degrees lower than downstairs - install cost ~ £0
   
5. Sealing the leaky ground floor floorboards - install cost ~ £2850
   
6. Insulating under the ground floor suspended floorboards - install cost ~ £1,300

The first graph shows the savings that you could expect by making each of the amendments on their own and keeping everything else constant - the boiler and the walls each are expected to save over 25% of energy bills.

If you add all of these up the total is not far off the total fuel bill costs of the house - yet none of them affect the electricity - alarm bells should be ringing.

Next we built a range of packages of measures and evaluated the net effect of each package.  The results and comparisons to what you would get if you just added the individual savings for the measure in each package together are show in the graph below.

As you can see the variance increases the more measures you add into the package - by the package with 7 measures the variance is around 30% of the actual savings.  In our Masterplans we often build packages with upwards of 30 measures so it's clearly essential to calculate the combined effect of recommended measures rather than just adding up the individual savings.

Do the regional variations in the climate of the UK have a significant effect on the potential savings from different measures?  We think so and that is why our Home Energy Masterplan modelling uses design weather years for different regions of the UK.

As an example we've taken a pretty standard 3 bedroom Victorian end of terrace in London (85m2 floor area), surveyed and then modelled it and then analysed the predicted effect of upgrading the boiler - an annual saving of £495 from an initial annual fuel bill of £1,766.

Background on the house:
Solid brick, no loft insulation, uninsulated solid and suspended floors
Single sash windows in good condition
Old boiler with permanent pilot light providing heating and hot water
Programmable heating on twice during the week and most of the day at weekends, thermostat set at 19 degrees throughout.

What we did next was to hypothetically move it around the country and carry out exactly the same boiler upgrade for the house in each location.

The image below shows where the different locations we chose and the graphs and figures show the £ sum of the variance from London over a 20 year timescale - chosen to represent a Green Deal style loan although it is expected that these may be up to 25 years.

These results are for single measures only and with everything else about the house and its use being kept constant.

We believe that the figures are large enough to make taking regional climate into account if accurate predictions are going to be made - especially if they have a financial implication.

In this cold weather we've heard quite a lot of news about condensing boilers breaking down, and condensate pipes freezing. An example article is linked here:
Thisismoney about condensing boilers failing during the cold snap.

We thought this article was a bit OTT for what is essentially occasional installer error on condensing boilers - which are in our experience usually good and reliable. It is however a useful article in highlighting this issue and gives us the opportunity to describe the solutions we've come across. Do feel welcome to comment with ideas / perspectives which may be useful to future readers.

If your pipe freezes, chance is that it is too small (20mm is common) or not steep enough. Ideally the pipe should be 32mm or more, and should fall quite steeply. Even so it may still freeze.

Further solutions we've come across people using successfully are to:
1 – put the pipe into an internal waste pipe (eg connected to sink pipe). This is probably the best solution.
2 – extend the pipe down into a drain that will be warmer due to bathwater / flushing loos / etc., being careful to ensure that it is positioned in a way that it won't become easily blocked.
3 – install pipe heaters (final option as these will use additional electricity - example product here). About 10W should probably do the trick.

The point about return temperatures is correct, and there is a related issue that old radiators will have been sized for a flow temperature of 85, whereas it’s recommended that a condensing boiler should use a circulation temperature of 70. This can occasionally lead to under-sized radiator problems and/or a drop in efficiency, but even so the non-condensing cycle of a condensing boiler is more efficient than older boilers running at optimum efficiency, and any decent heating engineer will check as part of the installation.

There is no data available on reliability of condensing boilers – we hear that British Gas collects this data but it isn't currently published, and no one else seems to have any data. We'd love to see some research on this if anyone is aware of any existing, or chooses to commission some.