Frequently asked questions

What do we mean by energy efficiency?

This is the management of how we use energy, specifically in relation to heating, lighting and ventilation within our homes, schools or places of work.  Usually the easiest efficiency saving we can make, is to reduce the amount of energy we waste, at a very basic level this means turning off anything which consumes power when we don’t need it (teenagers everywhere please note!) and to fit low energy lighting products.  The next, and usually biggest step, to energy saving is to improve the insulation of our buildings, this reduces the amount of heat we pump into the atmosphere.  This has a two-fold saving, it reduces the use of carbon fuels to generate the heat in the first place, and it also reduces the amount of heat energy escaping into the environment.   Once we have done the basics, we need to start looking at the operating efficiency of our energy consuming products.  It is not difficult to change light bulbs from the old incandescent type to new low wattage mini fluorescent or LED bulbs, and this can be done as a staged replacement as old units wear out, however replacement of major plant can involve a bigger capital cost.

New energy consuming domestic appliances come with an energy rating, A being the best and F the worst, all new central heating boilers are rated in the same way.  Fitting a new condensing boiler is a really good way of improving the efficiency of your home, as new boilers have to be fitted with a minimum level of control system to ensure they perform as efficiently as possible.  We can also upgrade existing heating controls to improve the efficiency of an existing system, most domestic heating systems fitted more than 15 years ago have very little decent control, and it is quite simple to remedy this.  Improving the level of insulation and control of the heating systems within our hom es will often pay back the capital cost in under 2 years, with huge reductions in carbon emissions.  To move beyond these types improvement in energy efficiency, we need to re-think the way we heat our homes.  Installation of a heat pump, solar panels or a micro combined heat and power (CHP) unit will massively reduce the carbon footprint of a property, however, the capital cost involved is often very high, and these systems may involve big changes to the existing ‘traditional’ heating system, for example to the use of thermal stores, fan coils or under floor heating.

What exactly is low carbon technology?

This relates to anything that reduces the amount of carbon we are responsible for releasing into the environment, mostly in the form of fumes from burning fossil fuels, oil, coal and their derived products.  There are many ways we can do this, often the simplest are the most difficult us to achieve within our current lifestyles, for example, walking instead of driving, but there are many things we can do with the infrastructure of our properties that would make big differences.  This starts with switching things off when we don’t need them and can involve major alterations to the heating and ventilation of our properties.  Anything which lessens the amount of fossil fuel we need to burn is a form of low carbon technology, whether that be use of wood burning heating appliances, rainwater harvesting or heat recovery ventilation systems.  Both of these last two are about making better use of energy, for example, in the case of rainwater harvesting, why flush toilets with water treated to be fit for drinking? In the case of heat recovery ventilation, why let all the warm air we have spent so much money and carbon carefully heating in our properties out of the doors and windows?

What is meant by renewable heat sources?

This is any energy source that does not rely on fossil fuels as its main source of power.  In domestic and light commercial heating we are dealing with primarily solar power, which is the ultimate renewable energy source, and sort of self explanatory really.  Wood burning appliances which utilise fuel from suitably managed forests.  In this case, the carbon released from burning the wood pellets is only what has been absorbed in the life of those trees, rather than the carbon laid down millions of years ago, from millions of trees.  This recently trapped carbon can be offset by planting new trees to replace the ones cut down to fuel pellet burning appliances.  Heat pumps, both air source and ground source, while not being truly renewable heating appliances, are considered micro generation appliances, because they use less electrical energy than the heat energy they provide.  Micro Combined Heat and Power units (micro CHP), these also are not really a renewable energy product, but even though they burn fossil fuels, they generate electricity, either for use at point of generation, or for export to the grid where it can be utilised locally to reduce the wastage inherent in the normal distribution of electricity via the National Grid.

What is the coefficient Of performance?

This term relates to the efficiency of a heat pump unit, and is normally abbreviated to COP.  If a COP is quoted as 2.8, this means for every kilowatt of electricity the heat pump uses when it is operating, 2.8 kilowatts of heat is generated.  It seems too good to be true, doesn’t it?  It happens because of the refrigeration cycle within the heat pump, which uses the electrical energy to create heat, which is given up to the heating or hot water system.  The key thing when a COP is quoted is that the source and output temperature must be quoted, so if you want to compare the efficiency of different heat pumps, the same source and output temperatures must be used. 

We are approved installers for Stiebel Eltron which is a German manufacturer that has been making heat pumps for over 25 years, as an example, they make an air source heat pump, romantically called the WPL13E.  This has a nominal output of 8.1 kilowatts.  This is at an air temperature of +2° Celsius, and an output temperature to the heating system of +35° Celsius. The COP at these temperatures is 3.4.  So to get 8.1 kW of heat from the unit, it would use 2.4 kW of electricity.   The operating range of the heat pump is –20° Celsius to +40° Celsius.  This temperature is only suitable for heating via fan coils or under-floor heating. It is obviously not suitable for hot water provision, however, the figures tell us that at the same source temperature, if the output temperature from the heat pump is +50° Celsius, then the COP drops to 2.7. 

This then has implications for how the system is installed and controlled.  If a heat pump is fitted to an existing  heating system with traditional radiators, then the heat pump will probably need to run at an output temperature of at least +50° Celsius.  This would mean that the COP would be lower than if an energy efficient, low temperature form of heat emitter were used.  If the heat pump is fitted to say under-floor heating throughout the property, then the output temperature for heating can be far lower, improving the COP.  The controls would then operate the heat pump at a higher output temperature only for heating the domestic hot water supply.  It is possible to install a mixed system, part radiators, part under-floor heating, for example, as the control unit with the heat pump is capable of adapting to the system to which the heat pump is fitted.  The thing to remember is that a modern (high efficiency!) condensing boiler operates at a COP of around 0.9, i.e. for every kilowatt of gas you buy, about 90% gets into the heating system.  Until now, because gas is nearly one third the price of electricity, air source heat pumps have not been much cheaper to run than a condensing gas boiler.  However, from 2010, the government are introducing new lower electricity tariffs for electricity supplied to heat pumps, this is likely to halve the running cost of a heat pump compared to a gas boiler.

How is the refrigeration cycle related to energy efficiency?

A heat pump operates using the refrigeration cycle.  This relies on the principal that when a gas is compressed, it heat up, this is the heat we get from a heat pump.  Inside the heat pump is a sealed circuit with refrigerant in it (often called Freon).  This is a liquid only below about –35° Celsius.  So the liquid is boiled by the heat source, whether that be air, water or the ground, via the evaporative heat exchanger.  The refrigerant gas is then compressed, and it is the compressor that uses most of the electricity in the heat pump.  As the gas is compressed, it heats up.  The gas is then cooled on the condensing heat exchanger, where the heat is transferred to the heating or hot water system and the refrigerant is condensed back into a liquid.  The pressure of this liquid is then reduced via a pressure reducing valve, the liquid is drawn back into the compressor and the cycle starts again.

Why is under floor heating so often talked about in relation to energy efficient heating?

These types of heating are particularly well suited to use with heat pumps because they are designed to operate at lower temperatures than traditional convector radiators.  If it is properly designed, under-floor heating is happy to operate at temperatures as low as 35° Celsius.  Under-floor heating can be ‘retro-fitted’, though this is often quite expensive, however in new properties, it is becoming a standard form of heating, especially on the ground floors.  If a ground source heat pump, with vertical bore holes for the ground source, is fitted to under-floor heating, it is possible in the summer to utilise the ground source to ‘passively’ cool the under-floor heating circuit.

By passive cooling, we mean using a heat exchanger between the ground source circuit and the under-floor heating to lower the temperature of the water in the under-floor pipes.  This does not require active refrigeration, like in an air conditioning unit, which can be expensive to run.  In this country this form of cooling is generally sufficient, as we do not experience prolonged periods of very high temperatures most summers.  Because it relies on the temperature of the ground source, which is usually around 12° Celsius, the only running cost of operating it, is that of the two circulating pumps.  The heat pump controller is able to handle the operation, as it is important that the floors are not cooled too much, otherwise condensation may form, which is not ideal.

What is a fan coil unit?

Fan coils are a type of fan convector radiator that is designed to operate at temperatures of around 35° to 40° Celsius.  They can also be used for either active or passive cooling.  For passive cooling the heat pump needs to be a ground source with vertical bore holes. Active cooling is what air conditioning units do, they actively refrigerate the air in the room.  Some air source heat pumps are designed to operate as both heating and cooling units, which means in the summer, they can act as a central air conditioning unit.  This means that if they are connected to fan coils, or ceiling cassettes (like normal air conditioning units), they can actively refrigerate the air in the building, as long as the fans can cope with any condensation which may form.  The benefit of this type of system, is that a central air conditioning unit has a better COP (it is more efficient) than the more normal, individual split systems.  Also fan coils can often be more easily ‘retro-fitted’ than under-floor heating.

What exactly is a condensing boiler?

This is the most efficient type of traditional boiler currently on the market.  They are more efficient than older boilers, because they recover more heat from the flue gases, this improves their efficiency to around 90% (equivalent to a COP of 0.9) We do not believe that we will be fitting many boilers in 5 or 10 years time as heat pumps and solar heating look set to replace them for efficiency and performance.  However, if you are interested in a replacement boiler either as an option or instead of a heat pump, we would be delighted to provide a quotation.

How is a fridge related to energy efficiency and carbon emission reduction?

This is an appliance used for keeping important and delicate food stuffs, such as chocolate, wine or beer cool.  In just the same way that your fridge cools important produce that you put in it, by extracting heat from the goods inside and then putting that heat out of the back of the appliance (just feel the back of your fridge or freezer), so a heat pump takes heat from the source, cooling it down in the process, and puts it into your properties heating system, or hot water tank.