Renewable Energy Devices Suitable for Underfloor Heating

Harnessing the Infinite

With fossil fuel prices as high as they are, most of our customers are asking us to quote for underfloor heating with heat pumps and solar panels. There are four main types of renewable energy; solar, wind, hydro and geothermal. The first three are completely free at the point of production, although obviously you will have to make an initial capital investment in the renewable energy devices required to capture and convert the energy into a usable form.

Solar & Hydro

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As the song says, "Where do I begin to tell the story of how great a love can be?" Yes, heat pumps and underfloor heating are truly a match made in heaven.

ground source heat pump photo

Ground source heat pumps
Heat pumps take latent heat energy from the ground or outside water and convert it into usable heat energy. They work like a fridge in reverse and run on electricity, so they're not, strictly speaking, a 'renewable' energy source. However, the amount of electrical energy required to run them can be considerably less than the usable heat energy they produce. A good heat pump properly installed and running at peak efficiency can have a heat output of up to five times the amount of electricity it uses. This is known as the 'Coefficient of Performance' or COP. Look for a heat pump with a high COP in its technical specification. However, do not be misled by sweeping statements of efficiency. Heat pumps are most efficient while providing warm water up to around 35 deg C. Above this temperature, the efficiency, and COP, will fall away dramatically, so if you are using the heat pump to run radiators in a draughty old house, they could be no more efficient than an oil boiler.

heat pump diagram

Surface collectors
The most common method of extracting the heat energy from the ground is through horizontal pipes buried a metre below the surface. At that depth, the soil temperature is fairly stable at around 10 -12 deg C. Surface collectors are the easiest and cheapest means of extracting the ground heat.

Ground probes
A ground probe, or borehole, can be used where there is insufficient room to have a horizontal ground loop. A specialist drilling company will need to be employed to drill the hole and insert the probe. This makes a ground probe much more expensive than a horizontal collector.

Ground water
If a lake or large pond is available it can be used as a heat source because the water temperature is always between 7 and 12 deg C all year round.

For a diagram of these scenarios, please click here.

solar hot water panels photo

Solar water heating
This is the most popular and cost effective way of capturing energy from the sun. Solar water panels are usually mounted on the roof of a building, which is orientated as near towards the south as possible, to derive the greatest benefit from the midday sun. Water is circulated through the panels and the heated water passes through a coil in the DHW cylinder where it heats the stored water in the cylinder.

Solar water heating is most beneficial between April and September, although a sunny day at any time of the year will provide a useful amount of hot water. The area of panels required is determined by the size of the hot water cylinder, which in turn is calculated on the size of the property and the amount of hot water needed each day. As a general rule, one square metre of panel is sufficient for 60 litres of stored hot water, although this figure will vary between manufacturers. Solar water heating only requires a small amount of energy to operate the circulating pump, although some systems have an integral solar powered pump that starts to operate when the sun is shining, so does not require an electrical supply.

Solar photovoltaic cells
Solar electric (photovoltaic) panels mounted on the roof convert sunlight into electricity. A large surface area is required to capture enough energy to be worthwhile, but these panels are currently very expensive to install. The price is likely to fall as product development improves efficiency, and demand increases production.

solar photovoltaic cell photo

Small domestic sized hydro generators are available, but are only suitable in applications where there is a sufficient constant flow of fast running water with a fall of preferably not less than one metre; a higher fall, and large volumes of water, would provide a greater amount of energy. Anyone who does have a stream or burn running through their property could certainly consider this option, and if feasible, this could provide a reliable uninterrupted electricity supply.

hydrodynamic screw diagram

Air source heat pumps
If there is insufficient room for either horizontal ground loops or a bore hole, then an air to water heat pump can be used. These units are installed outside and convert the air temperature into usable heat energy. Air to water heat pumps are not as efficient as ground source heat pumps, but in a well insulated building, they should be able to provide all the heating and hot water requirements throughout the year. It is not unusual to dock an air source heat pump with a conventional boiler, which would only come on during the coldest weather when the heat pump cannot satisfy the demand.

air source heat pump photo

A roof-mounted wind turbine can generate a small amount of electricity to offset the consumption from the grid, but this is unlikely to be sufficient to make a house self sufficient in electricity. For those people fortunate enough to have a windy site (and planning permission) a mast mounted wind turbine could provide enough electricity to satisfy a domestic demand. The obvious disadvantage of a wind turbine is that it only produces electricity when the wind is blowing, so you will still need to be connected to the grid or have a back-up storage or generation facility. One of our clients has a mast mounted wind turbine and a battery storage facility, which has enabled him to be totally off the grid.

rooftop wind turbine photo

Back boilers/Multiple sources
Wood burning, or other stoves with a back boiler can be coupled to a heating system via a thermal store, or buffer cylinder. The volume of the thermal store must be big enough to prevent the back boiler from overheating. A number of different heat sources can be connected to the thermal store, which can then provide hot water to the heating circuit.

solid fuel stoves photo

Schematic diagrams of various plumbing arrangements of underfloor heating with heat pumps and solar panels.


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