From 12,000 kWh/yr to under 2,000kWh/yr for home heating.

 By Pat Hackett.

One of my goals is to make suggestions on how individuals can reduce energy consumption so that  collectively we need less power stations in the future to meet demand making the task of replacing them with renewables less of a challenge. Furthermore to do this without a loss in individual wellbeing.

I recently set out to see if we could continue to reduce our energy consumption for home heating on the realisation that this is one of the most effective way individuals can reduce our impact on the climate without waiting for Energy companies or the government to take adequate action on climate change. Many of the low cost, high impact ways that could be replicated throughout the country are of course well known. However I also found ways involving zero cost! that had huge impact for those who have heat pumps installed. I could not find any previously written descriptions of these ways. The engineers who designed the hardware and software must clearly have full knowledge to have allowed the installer to make changes to the relevant parameters but there seems little or no communication on how the user can get the best combinations. I felt it worthwhile therefore to make a start on including some of these ideas in this post.

Before the overall project was started we already had a gas boiler for domestic hot water (dhw) and space heating that adequately heated our 4 bedroom semi-detached cottage. This was a stone built, 200 or so year old building with a converted loft above the ground floor. We already had double glazing throughout and some draught-proofing and insulation. Also we had already  converted our bathroom to a wet shower room. 

Although, after additional draught proofing and insulation as described in this post, an EPC indicated space heating and dhw would require over 20,000 kWh per year of energy.  This was assuming three people using hot water and the lounge heated to 21C and all other areas to 18C for something like 11hrs per day and 8 months per year! The home had previously required about 12,000 kWh of energy per year but this was for two of us and only heating public spaces to a comfortable 19C. A weak point was perhaps the shower room in a North-East facing extension on very cold mornings or on some Spring days when little or no other heating in the home was needed. This shower room was heated with a towel rail  type radiator using the central heating system. We had already converted our bathroom to a shower wet-room but it took over a minute for hot water to reach the mixer shower from the gas boiler.

So  for good reasons (why-i-removed-gas-boiler-for-air-source heat pump )the plan was to replace the gas boiler with an air source heat pump for space heating and work out the way to get hot water for our needs while minimising energy demands.

The steps that follow were done in chronological order. After a winter of all the improvements being completed the heating demand can be readily estimated to be under 2,000 kWh/yr for all space heating and dhw and with improved comfort.

1. Draught-proofing.

While not going overboard to the detriment of adequate ventilation this is probably the cheapest way to lower consumption that should be done regardless of the heating system. We draught proofed or checked round external doors including around internal vestibule doors leading to the external doors, windows, under skirting boards and chimney balloons in rooms with fireplaces.

2. Insulation.

A DIY insulation of the loft was done to EPC recommended standards. This was to insulate the sides and top of  a previously built loft conversion. The sides of this attic room allowed improved insulation of the ceiling of the ground floor rooms.

Internal insulation of the original external walls was not done due to the lower impact, higher cost and uncertainties such as dampness perhaps becoming an issue.

(It was after this an EPC estimated 20,000 kWh/yr for heating and dhw.)

3. Radiator sizes.

Some of the radiators where replaced with larger radiators where necessary. This would enable the central heating with the heat pump to have lower flow temperatures  which in turn increased the efficiency or coefficient of performance (COP) of the heating system. (Link to follow)  Also counterintuitively this did not impact on useable wall space but rather the reverse (as will be explained in the link) and contributed to the improved comfort feeling. 

4. Installation of an instantaneous electric heater for dhw.

This is an example of when low consumption sometimes outweighs the advantage of high efficiency conversion. There is little point in creating energy efficiently if the advantages are lost by inefficient use. By having a smart instantaneous water heater we heat the water largely where, when, how much and to the precise temperature. The onboard meter indicates a consumption of less than 1 kWh per day! This means no need for a dhw tank. (Do I need a hot water tank if installing an ashp)

5. Installation of the heat pump.

An air source heat pump can have efficiencies (expressed as coefficient of performance or COP) well above 300% (meaning a COP greater than 3). The installers did this superbly from fitting the heat pump to a small internal heat exchanger and to a centrally located buffer tank minimising the hot water pipe lengths thereafter to the radiators. The central location of the buffer tank meant that any waste heat from the tank was systematically used to heat the home precisely at the time when needed. Also a weather compensated control panel was installed allowing optimum lower temperatures to be achieved  (explained later in this post) again increasing the COP of the system.

6. Optimum use of the system control.

The biggest factor that improves the efficiency of the water heater is having higher outside temperatures which is of course outside your ability to control. The next most important factor is having lower temperatures for the flow of water in the radiators which is in your control. (It is important not to confuse having low radiator flow temperatures with not having the desired room air temperature to be achieved of course). Much lower radiator temperatures can easily double the amount of renewable energy your heat pump can create compared with having perhaps unnecessary high flow temperatures. The manufacturers and the installers will have largely ensured lower temperatures but the user can considerably help with wise use of the system.

So finding as many ways as possible to reduce the radiator flow temperatures while still achieving the desired room temperatures and comfort is the goal (and a good example of the creativity of good engineering). Increasing radiator surface has been addressed above and has the advantage of being able to reduce the flow temperature while still giving out the same rate of heat energy. If the rate of heat energy is the same there is no loss of responsivity (meaning how quick the room temperature can be increased). So what are the other ways that the flow temperature of the radiators can be decreased?:-

a). Making optimum use of the weather compensated system control.

If the outside temperature is low or you increase the desired target room temperature ( demand temperature) you will need higher flow temperatures to heat your home. Of course the reverse is true and this means the radiator flow temperature can be reduced in warmer weather or lower demand automatically along what is known as a heat curve. Getting on the optimum heat curve therefore is very worthwhile and probably the most important aspect to get right for optimising your controls. Your installer will have selected a likely heat curve based on your building dimensions including walls doors and windows, insulation and radiator sizes. However it is best to modify this by seeing how your heating system behaves in practice and this can take a little time and thought. If you select too high a heat curve an inbuilt thermostat controlled by the desired room temperature on the system control could still ensure a fairly stable room temperature. However this is analogous to driving along a road using unnecessary acceleration then braking when a steady speed would suffice. Just like your car the heating system will be working less efficiently and with reduced lifespan. Alternatively if you select too low a heat curve your system will be unable to meet your demand temperature. Getting the right "Goldilocks" temperature will be easier to find if you check this in darker winter days when there is no random solar gain through windows. (Also best to do this also when there is no random heat from other appliances). Once you have the heat curve selected the flow temperature will adjust automatically to the optimum throughout the year (unless you then changed your insulation or radiator sizes dramatically).

b). Switching off the thermostat function from the desired or target room temperatures and instead relying on temperature modulation to stabilise the room temperature.

With thermostatic control your heating is switched off when your desired temperature is reached. This means the compressor and the pumps circulating water through your radiators are stopped and your radiators cool down. Typically your air temperature will need to cool down by as much as about half a centigrade degree before your heating comes back on. This delay is automatically achieved perhaps by your control system using your room temperature as signals. If this delay or air room temperature hysteresis cycle is not incorporated your heat pump could instead rapidly cycle, switching off, on, off etc. drastically reducing its lifespan. This inclusion of hysteresis is also the kind of approach used in a typical gas boiler central heating system to prevent rapid cycling but could be much more of a problem with a heat pump with a large powered compressor. Using a thermostat with this air room temperature hysteresis however, can mean your radiators heating for half an hour and then off again for half an hour, and so maintaining an approximate stable temperature. With a heat pump there is an additional incentive to remove this air room hysteresis while still preventing rapid cycling because there is also a gain in efficiency by achieving the same heat output more steadily without swings requiring higher temporary temperatures.  If no thermostat function is active the heating system will not switch off but IF set up correctly the radiators will provide just the same amount of heat energy delivered more evenly over time with a lower maximum required and achieve stabilisation at (or very close to) the desired room temperature. 

The correct set up to enable temperature modulation to stabilise requires your radiator flow temperature to be just at the right temperature and at least theoretically this can be achieved by being on the right heat curve alone whereby the minimum temperature is selected for any particular outside temperature and demand room temperature. On achieving the desired room  temperature your home will be losing heat at the same rate as provided from your heating system. This could result in a very unresponsive or slow to change heating system however; that would also be difficult to stabilise when other secondary factors like wind speed or direction or windows or doors opening etc could affect the heating.

Selecting temperature modulation without thermostatic control achieves what good engineering wants :- the best of both worlds. If your room temperature is below your desired room temperature the target flow temperature in the radiators is increased by amount in proportion to how far your room temperature is below and if your room temperature ends up for any reason higher than your target room temperature your target radiator flow temperature is reduced again in proportion to the difference. This is how a stabilised temperature is maintained at the desired room temperature selected. (Unless of course other heat sources such as solar gain through windows causes the desired room temperature to be exceeded as discussed later in this post.)

This means that by being on the optimum heat curve and using temperature modulation your radiators are working at their most efficient with minor temperature boosts only temporarily used when required.

This is a brilliant, simple and effective example of what engineers would call negative or stabilising feedback. (Although I have to admit I have never seen anyone else describe this modulation that way).

It must be said that using temperature modulation without thermostatic control is less intuitive than with thermostatic control for the reason that the heating doesn't completely switch off at the desired room temperature or even a bit above that. You can use this to your advantage however. Like many people we have a lower desired room temperature during the day than the evening. By using temperature modulation I can select a lower set back temperature overnight that will ensure the room temperature gradually drops from the higher evening room temperature to the desired lower day temperature in the morning without needing to set it for a few hours earlier and rely on less efficient thermostatic control. Once this set back temperature is found, (it took me two attempts to home in) the same set back temperature will do the same job on any day that heating is required regardless of the outside temperature thanks to the heat curve using the weather compensated system. So what is happening to the radiator flow temperature overnight? The modulation means that when the evening temperature is set back the heating may go off or the radiators continue to heat with  a very low target flow temperature perhaps in the low twenties centigrade! This is because your room temperature is quite a bit higher than your set back temperature and the temperature modulation ensures that instead of switching off your heating works at a much reduced flow temperature. The system will be working on maximum efficiency. As the night continues the temperature outside will likely drop and, at the time of year when heating is required,  your room temperature will definitely drop. The heat curve with temperature modulation will therefore ensure that as morning is reached your target flow temperature will gradually increase just minimally as needed thanks again to the temperature modulation. Your day time temperature can be maintained onwards from here as previously explained.

If you have temperature modulation stabilisation you can be assured that if or when the heating needs to come on it will  always do so in advance of your room temperature dropping to the set temperature at a low compressor power and starting with the lowest target radiator flow temperature. With thermostatic control this will not be the case putting undue stress on your heating system.

Throughout late spring, summer and early autumn your room temperature during the day is likely to exceed your selected desired room temperature due to variable unpredictable solar gain. To maximise on this gain and to simplify the temperature settings at a time when your energy consumption will be much lower it will likely be easier to have thermostat control selected as opposed to temperature modulation without thermostat control during this time. (Note. A system control may now replace what most people would call a programmable room thermostat. Also the latest system control from Vaillant describes thermostatic control as "expanded" temperature modulation in the installer's manual.)

So at times of the year when your room temperature is largely dependent on your selected desired room temperature setting as is the likely case in Winter then temperature modulation without thermostatic control is ideal. At times of the year when your room temperature is largely not determined by the selected desired room temperature thermostatic control (or expanded temperature modulation) can be simpler and more appropriate.

 7. Getting the advantages of gradual heating using lower radiator temperatures.   (Future link )

When you require your room temperature to be increased for comfort, the lower radiator temperatures that arise by being on a low heat curve will mean you will need to  arrange that further in advance but this extra energy may only have a small impact on consumption if your home is well insulated. If you use the benefits of gradual heating from lower temperature radiators as well as the efficiencies described by being on the optimum heat curve and by using temperature modulation you will more than compensated for this.

When you increase the desired room temperature the low target flow temperature will heat up the water in your radiators and buffer tank to a new higher level. The air room temperature will gradually increase but it will also gradually increase the temperature of the walls and furniture. The slower rise in room temperature may take a few hours to get to your desired level but unlike high temperature radiators that heat your air quickly leaving the surroundings "behind" you will have taken the walls and furniture up in step. This means that you are likely to have less cold spots and you benefit from longwave radiation from the surroundings all around you. This means you will feel more comfortable even at a degree of lower air temperatures. The heat doesn't all "get lost" in the walls and furniture and what you may well find is that you can set back the timing of your "target" room temperature a few hours earlier! (On colder nights there will also be more energy in the radiators and buffer tank that you had to increase in advance. Temperature modulation will ensure that is given back before the lower target flow temperatures are reached and thus roughly the same advance in the set back time will work.)

8. Maximising on waste heat or solar gain.

 The goal is to aim for low consumption not just high efficiency.

a) The location of our buffer tank in a purpose built cupboard into the kitchen but with access from the corridor is a good example of systematic heat gain. The heat loss from the buffer tank mainly heats the kitchen only when heating is needed since our temperature tank will only be heated when space heating is required. This kind of gain can be verified with an infrared detector which shows the temperature of the walls to the kitchen from the cupboard to be 0.5 to 1 degree C higher than any other walls when the heating is required. (Incidentally this gain woul NOT show up on the COP or efficiency because the COP would just be the same if this buffer tank where placed in an outbuilding with none of the waste heat utilised.)

b). Utilising heat gain from other appliances such as when cooking.

This is not systematic heat gain because it doesn't happen automatically when you heating is on but it is predictable heat gain in your control. We find preparing our evening meal can usually increase our room temperature by about 0.5C (and sometimes higher) and so the default target room temperature is set 0.5C lower. If we are out then there is no problem and on occasions the room temperature can be tweaked temporarily up if needed.

c). Utilising solar gain.

Whether rooms are being used and needing heating, it of course makes sense to open and close curtains appropriately.  Also we benefit from doors to solar heated areas such as to a conservatory being left open when appropriate. This solar gain can be underestimated since this gain, when it can be utilised, can exceed that of solar panels on a roof. The windows can absorb most of the radiation of the sun unlike solar panels. During the daytime in Spring is the most likely time when this free heat can be maximised. It is a time when the outside air temperature is often low but the solar radiation is high.

This is a time however when using weather compensated modulation without thermostatic control can be a bit less intuitive. The target flow temperature in the radiators is largely determined by the outside air temperature but the room temperature is less dependent on your heating and more on the unpredictable levels of sunshine. Gaining full advantage of this solar gain could be more intuitively gained by reverting to thermostatic control.

 9. Addressing the temperature of the shower room.

After installation, the shower room temperature remained as problematic as it was before. Not warm enough on the coldest mornings or on some Spring days when little or no heating was required in the rest of the house.

Clearly having a larger radiator in the shower room would not solve the later problem. In any case making room for a larger radiator was a bit problematic anyway in terms of available space.

Conventional zoning using the central heating system might be considered an option. A problem here is that asking your heating system to heat only a small volume of water in your radiators is difficult to achieve without increasing the risk of rapid cycling or ensuring that the heat is used efficiently regardless of how efficient it was made.

A practical way to both minimise energy consumption and making it far more convenient is to effectively zone the system by having a separate additional heating system:-  A high temperature 350 watt far infrared ceiling mounted panel.

Far infrared means it is not near the visible spectrum like short wave infrared heat you feel from direct sunlight. It is similar or slightly hotter than a high temperature radiator that would be typical in a gas central heating system turned on to maximum. Since these panels use direct electrical heating with no heat or circulating pumps there is no air hysteresis cycling issue and hence can be switched off and on rapidly to maintain a stable temperature if required using thermostatic control. However I use this one on a short timer with no need for the thermostatic control. These panels are excellent as personal  heaters when there are no objects between you and the heater and you will feel the heat within minutes of switching on. These panels will not have the efficiency or high coefficient of performance as the heat pump system but will be near 100% efficient at point of use. Used on a 15 minute timer this heater adequately boosts the heating in the shower room using less than 0.1kWh without allowing the shower room to dictate the temperature and time settings for the rest of the house.

In summary having a well insulated draught free home with an air source heat pump for space heating using optimum control settings and low temperature radiators, an instantaneous electric water heater for domestic hot water and a low powered but high temperature personal electrical heat panel makes our home very comfortable allowing hot showers whenever needed. Futhermore this is using six times less energy than previously and even less than that as estimated by an Energy Performance Certificate. There must be a lot of power stations nationwide that are not needed.

Link page for further or future related posts.

If thinking of making changes to your home heating it is best to get impartial advice.

In Scotland I would strongly recommend Home Energy Scotland.