What are CHP boilers?

Combined heat and power (CHP) boilers produce both heat and electricity in one single process. This process is sometimes referred to as cogeneration and the technology that supports it has been around since the 1970s, but has mainly been confined to industry and large dwellings such as hospitals and sports centres.

As the price of fuel has increased over the last few years, it now makes economic sense to bring CHP technology into the domestic setting.

A micro-CHP boiler is defined in the EU Act on Cogeneration as a domestic unit that is limited to 50kW of capacity.

The different types of CHP boiler

There are three types of micro-CHP boiler:

The Stirling engine CHP boiler

The Stirling engine CHP boiler is a type of external combustion engine, where the combustion engine is heated when the boiler is fired up to produce the hot water. This heats up the fully enclosed working gas within the Stirling engine, causing it to expand. The expansion of the working gas forces a piston to turn up and down between a copper coil, generating an electrical current, which can then be used in the home. The working gas usually used in a Stirling engine is helium, due to its strong heat transfer properties.

The main limitation of this type of boiler is that it only produces electricity when you have the central heating on, so despite being a very efficient type of boiler, it does not produce an abundance of electricity. A key advantage is that the combustion process involved in a Stirling Engine CHP boiler is much quieter and more efficient than internal combustion engines.

The internal engine CHP boiler

This type of CHP boiler is commonly used in large dwellings such as hospitals. It involves using a fuel source to drive a turbine, which is connected to the electricity generator. The waste heat from this combustion process is captured to produce hot water for the space heating and warm water. This is the most common form of CHP boiler found to date. However the process is noisy and you have far less control over the hot water generated, so fuel cell and the Stirling engine CHP boilers are often preferred.

Fuel cell CHP boiler

Fuel cell CHP boilers use fuel cells which convert fuel and air directly into power and heat through a quiet, efficient, solid-state electro-chemical reaction. A video demonstration of how a fuel cell CHP boiler operates in the home can be found on the Ceres Power website.

Fuel cells generate power significantly more efficiently than internal combustion and Stirling engine CHP boilers. This is because fuel cell CHPs convert chemical energy directly to an electrical current, maximising their efficiency.

This type of CHP boiler is still in development so is not yet commercially available on a wide scale.

How CHP boilers work in the house

A home would typically use a boiler to meet its heating and hot water needs only, and then source its electricity from the grid. Central generation wastes a significant proportion of the energy it creates, through heat losses in the power station and in the transmission and distribution network.

Micro-CHP boilers avoid these losses, and capture the heat for use within the home. This efficiency can save the consumer around 25% of total energy costs (around £600 off your bill if you have a typical 3-bed semi-detached house), and reduce each home’s CO₂ emissions by up to 1.5 tonnes per annum. Micro-CHP boilers are designed to generate all of the heating and hot water and a significant percentage of the electricity needed by a typical UK home.

The CHP boiler can use a variety of fuel options including the gas that is supplied by your current provider, but also hydrogen, LPG & biofuels. Even during the summer when the home’s central heating system is turned off, the heat produced by the micro-CHP boilers when generating electricity can be stored in a back-up hot water cylinder and then used for domestic hot water. Therefore the micro-CHP boilers are capable of operating all year round, maximising energy bill savings 365 days a year.

Micro-CHP boilers are designed to one day replace your normal condensed boiler, using the same types of connections; they also have similar installation and maintenance requirements. A micro-CHP boiler only requires one connection to the electricity network in the house and it’s ready to go!

Industry development

Micro-CHP boilers are an example of a microgeneration product for the home. The UK Government has estimated that microgeneration products (such as micro-CHP boilers) have the potential to supply over 30% of the country’s total electricity needs and help meet its international environmental obligations, such as the 2020 EU carbon emission reduction targets. Owning a micro-CHP boiler is one step in the right direction. Full costs in the UK of a micro-CHP boiler including installation are yet to be made fully transparent; however incremental cost estimated in the region of £2,500 to £3,500 versus a condensing boiler, therefore a full installation is then estimated at between £5,000 to £7,000.

Research commissioned by the Government has shown that micro-CHP boilers have the potential to become the micro-generation ‘system of choice’, replacing the condensing boiler, which is the standard system in most UK homes today. Commercial experience has also shown that realising the benefits early pays off the most over the long-term.

Currently only the Stirling engine-type micro-CHP boilers have been made available on the domestic market. For example the Baxi Ecogen product is one of the few available micro-CHP boilers that is commercially viable and available for the home. By the middle-end of this decade, the expectation is that fuel cell models such as the Baxi Gamma 1.0 will be fully available to the UK consumers.

When fuel cell micro-CHP technology is commercially available, the consumer should see the price of Stirling engine models fall. In addition with the competition in the fuel cell space (Baxi, Ceres Power, etc), this should also make those models commercially competitive. Current evidence suggests that the take-up in UK homes has only been limited, with a lower number of Micro-CHP boilers currently installed in the UK than expected by the government – as opposed to Denmark and Germany where the technology has been more widely adopted.

CHP Boiler Technology Summary

The following list is a quick summary of the CHP boiler features:

• Delivers central heating, hot water and electricity
• Simple to install, replacing an existing gas boiler
• Easy to use with automatic operation
• Can use the same gas supplied by British Gas, NPower and other gas providers
• Lifespan of the fuel cell boiler, yet to be determined (but typically 10-12 years)

Remember micro-CHP boilers are efficient because they generate heat and electricity in one place. They will save you money and help the environment. Currently only the sterling engine type of CHP boilers are available to the residential market (internal engine CHP boilers are available for large properties), but in a few years’ time fuel cell micro-CHPs will also be available. Micro-CHP boilers are a strategic domestic technology for micro-generation that will help homes with their energy needs, but also help the UK (and other EU countries) meet external carbon emission targets.

Benefits

• CHP boilers are more environmentally friendly, reducing a typical home’s CO2 (carbon dioxide) emissions by up to 1.5 tonnes per annum in the UK.
• Mounting a CHP boiler can help you reduce your energy costs by 25% or more.
• Most CHP boiler manufacturers have partner agreements with the major suppliers (e.g. with British Gas) who provide installation services. Potential customers should check first with the manufacturer if you would like to arrange their own private installation.

Limitations

• The payback on the premium, which is the additional cost of a CHP boiler versus a condensing boiler, can pay for itself over the product’s lifetime. Note: Research in this area is not extensive as there are currently only a few commercialised producers of domestic CHP boilers.

Cost

• The full cost of installing a CHP boiler is somewhere between £5,000 to £7,000, depending on the type of installation and home specification, which is quite a big investment for a typical household.

1. Loft insulation

Loft insulation is one of the most popular ways to improve the energy efficiency of your home. It can be very cost effective, making an instant impact on the comfort of your home. The loft insulation helps to stop heat escaping through the roof of your house, which means that you will need to use less fuel to heat your property. You can save up to £150 off your heating bills each year and this can payback anywhere between six months and two years.

There are a few installation approaches you could take with this – you can either do-it yourself; speak to your energy provider to see if they offer loft insulation, or actually call a professional to install it. The do-it-yourself and the energy provider routes can save you quite a bit of money as the actual material is cheap.

The most common way to install insulation in your loft is to take mineral wool and firmly place it between the joists of the loft floor. The process is not very time consuming and the payoffs are very good. If you want to use the loft space, then you may want to place floor boards on the top, which will obviously be more time consuming.

2. Water Tank insulation

New combi boilers don’t have hot water tanks, but both system and heat-only boilers do. These hot water tanks, as the name suggests, store hot water so it is ready to use as and when you need it.

If you can imagine a freshly boiled kettle, the water fairly quickly cools down if left alone, so you need to re-boil it for your next cup of tea. In the same way, the hot water sitting in your hot water tank will cool down fairly quickly. By fitting a water tank insulation jacket to your boiler, it will dramatically decrease the amount of heat that escapes.

For £15 you can buy a hot water cylinder jacket that is easy to fit around the tank yourself. This could save you as much as £35 a year, taking under 6 months to pay back.

3. Draught proof chimney

If you have ever stood next to an unlit open fireplace in the winter you will probably have noticed a cold draught coming out of the hearth. Not only does cold air drop down the chimney, hot air rises – so the expensive heat that is produced by your heating system escapes up the fireplace.

By inserting a chimney balloon up into the chimney, it stops the heat escaping and cold draughts entering your house.

The chimney balloon is essentially a bag which is designed to be inflated about one foot up the chimney creating a thermal barrier preventing cold air coming down the chimney and hot air from your heating system escape.

In addition, the benefit of using a chimney balloon as opposed to blocking the fireplace is that you still keep it’s aesthetic beauty.

A chimney balloon costs about £20 and is very simple to fit. It is thought that as much as 80% of the heat in a room can be through a chimney, therefore fitting one can save you a great deal of energy.

4. Thermostat in the main living room

Installing insulation in your roof will prevent heat escaping through the roof, therefore increasing the ambient temperature of your house. However, to see the savings on your energy bills, you will need to keep the temperature the same before and after installing insulation – since you are then using less fuel to keep your home at that temperature.

A thermostat is an excellent way of closely controlling the temperature of your room, so on a warm day your thermostat will ‘speak’ to your boiler and tell it to produce less hot water for heating. Conversely, if your home begins to drop in temperature, the thermostat will fire a signal to the boiler to increase the temperature of the home, so it returns to a comfortable level.

A simple thermostat fitted in your living room can cost from as little as £150 and will save you on average £70 a year, so payback will be a little over 2 years.

5. LED light bulbs

If you have read our blog on buying the right LEDs, you will know that there are good and bad LED light bulbs.

If you purchase a higher quality LED bulb – which may cost in the region of £15 each for a GU10 bulb, it will last for between 20 – 25 years. A higher quality LED bulb will use on average 85% less energy than their equivalent incandescent / halogen bulbs, saving £8 or more each year. If you replaced 10 bulbs at a cost of £150 pounds, you may save £80 per year off your energy bills, and so after that have paid for themselves in 2 years; you will then see the saving benefits for 20 years or more going forward.