Combining Traditional and Renewable Heating Systems

Traditionally, the solution to heating our homes and its hot water was using oil boilers, topping up with electricity, as needed, and a roaring open fire (with or without back boilers) in the sitting room. There is nothing wrong with an oil boiler, as long as it is efficient - 10 year old boilers are not. Back boilers are an improvement in that you are at least getting more out of the fire than the little bit of heat it supplies the room. Electricity is the most expensive heating solution and should be avoided at all costs

Where am I going with this? Convergence!

In the past, we looked at heating solutions in isolation, ie: the oil for the water and the back boiler for those couple of radiators, etc. We need to start thinking about combining heating solutions in cost effective ways that benefits the most from each type individually so that the combined solution is efficient and effective.

Renewable energy sources like air source heat pumps (air to water) combine well with existing (efficient) oil boilers. The expensive part of heating water is the first 20-30 degrees (just listen to your kettle struggling at first). After that, the water’s temperature is easier and therefore cheaper to raise and happens more quickly. Have a look at the Ecodev renewable energy page for a practical description of what these are and how they can help you

Air to Water Heat Pumps use the same technology as fridges and effectively draw the heat from the air, even at -3°C. They are cost effective up to 30°C; the expensive part of heating by oil or electricity. At 30°C, the oil boiler fires up and heats the water for the existing radiators up to the 60°C+. Add solar panels into the mix and annual savings add up even more.

Geothermal aka Ground Source Heat Pumps do the same job as Air Source Heat Pumps, they just get their heat from the ground or ground water. To be effective, you either need the long ground loops placed below frost level at around 1.5m or sink a couple of bore holes to take the benefit from the more constant heat of the water deeper in the earth.

Condensing Boilers are up to 97% efficient compared to the 60-70% of standard boilers (and worse if older than 10 years. Even if 75% efficient, you are still throwing away one quarter of each tank of oil, about €150, each time you fill it. Condensing boilers re-use heat that is given off in the process of heating up the water and together with improvements in the way they operate makes them that much more efficient. They also happen to be a lot quieter!

Solar Panels come in many shapes and forms and some are more efficient than others. Evacuated tube panels are the most efficient, flat bed are the most aesthetically pleasing. In the northern hemisphere, optimum orientation is within 15 degrees of south and a 30 degree pitch is the most efficient, followed closely by a 45 degree pitch roof.
If evacuated tube type, check that the tubes are at least 60mm diametre and compare how many tubes you get per metre length.
For all types, check if they use copper tubing in the manifold? What insulation is around the pipe carrying the water to the cylinder? Is the cylinder a well insulated stainless steel type. Is there provision for a third coil in the cylinder for future upgrades? Is the cylinder at least 300litres (for averge family)? Ask for proof of the kW output of the unit, per metre squared, so you can compare apples with apples.

You need to use hot water to make a solar panel work for you. Eg: If you only shower and have a Triton type shower that produces it's own hot water, you will not be needing much hot water apart form the washing machine (if it does not heat it's own water). Payback periods will be that much longer and you will be better off improving some other aspect of efficiency in your home.

Heat Pumps are very efficient and they cost more than conventional oil/gas heating systems.

Payback periods are as follows:
Ground Source Heat Pumps: about 18 years
Air to Water Heat Pumps: about 11 years
Efficient Condensing Oil Boiler & rads: about 7 years
Solar Panels: about 3 years

Of course these payback times are dependent on the efficiency of the rest of the elements making up the house - the building envelope needs to be seen as a unit, made up of different parts that need to complement each other and the whole. Effective controls need to be put in place to determine and check how much heating is being provided and only when you need it. This prevents unneccesary heating and waste

One week link and the rest are affected, eg: build a very efficient timber frame or ICF house, with Geothermal heating, Solar Panels and Heat Recovery Systems, but save money by putting in single glazing (or any non A-rated windows and doors) and all the heat will leave via this weak link

So why these heating systems not commonly done?
Necessity for more efficient systems has recently created more effective, cheaper solutions. Lack of understanding of the individual elements and how it all fits into the bigger picture has created a wariness to start. Regulations have only recently started inforcing implementation in new builds and the escalating price of fossil fuels will do the rest

Ecodev provides energy efficient designs, energy usage consultations and BER certification.