Heat pumps are proving an increasingly popular renewable-energy heating system. Peter Gammon, technical product manager at MHS Boilers, gives some handy hints to aid smooth specification
The right heat pump -1
As with any specification, it is important to get the preparation and planning right to ensure the heating system is effective and
efficient.
It is no different with heat pumps. Before specifying which heat pump you need, you have got to know what the system demands are going to be and how you're going to utilise the heat pump.
From ground or water source to air source, there are plenty of heat pumps to choose from. If you're looking for a system which avoids the need for installation permissions or looking to meet your renewables commitment without a large capital outlay, then an air source heat pump may fit the bill.
But, if you are looking for higher outputs and have enough space available for the ground collector or suitable site for a ground probe, a ground source heat pump would be an obvious choice.
And don't forget some heat pumps are reversible and can provide cooling. With so many choices out there, it does pay to do some research before specifying.
Check on permissions- 2
We all despair of bureaucracy these days, but there is likely to be some permissions to be needed in the planning process - particularly with ground source or water source heat pumps.
The good news is that you'll often find the subject of renewables is welcomed by local authorities who are keen to be seen to be doing their bit for the environment. Bear in mind too that, if you're planning a water source heat pump, you will need permissions. And you will possibly need to talk to the Environment Agency. The main thing is to talk to everyone involved - they are often keen to see renewable energy in action.
Installation site-3
When it comes to installation, there are various things to consider. For example, with a 15kW ground source heat pump using a 32mm tube, on average you would likely need a collector length of 330 metres; so that is three ground drillings of 110m deep. So you'll need to plan access because ground-drilling machines are large and heavy and you must check the geology of the site.
Heat pumps are generally larger than domestic boilers and are floor standing, so you'll need to plan the plant room carefully.
With air source heat pumps, consider where you are going to position the inlet and outlet air louvres; there are special sound attenuated grilles available if
necessary.
Air Dest heat pumps-4
Air source units are the simplest to install because there are no earth probes or ground collectors to install, and there are versions that can be installed externally to the building.
Flow temperatures up to 55ºC can be delivered at outside air temperatures as low -10ºC, so air source units in the most areas of the UK are very viable heat generators for use with under-floor heating.
Naturally they come in various outputs, and their coefficient of performance will vary with operating conditions. There are a many types and prices out there, so go with a supplier which has a commitment to quality and technical know-how.
Ground source pumps-5
Like air source heat pumps, there are a number of ground or water source heat pumps available.
Get involved with the supplier or manufacturer to understand how the particular units perform and how they will work with the system you're specifying. If possible, try to get some training and that way you'll be able to have a good understanding of what is available as well the technical back up.
the right collector-6
The collector for a ground source heat pump comprises pipe buried in the ground, either in a borehole or a horizontal trench.
The pipe is a closed circuit and is filled with a mixture of water and antifreeze, which is pumped around the pipes absorbing heat from the ground. The ground loop can be vertical, for use in boreholes, horizontal, for use in trenches or a spiral, coil or slinky type, which is also used in trenches. Naturally, your choice will depend on the ground conditions and the amount of space available to you.
The buffer vesser-7
A buffer vessel is vital to an air source heat pump system. Not only is it used as a source of heated water for defrosting purposes but also to avoid the compressor having to start too many times.
The heat pump compressor shouldn't start more than three times per hour (or every 21 minutes). The buffer capacity should therefore be sized in relation to this. The best way to make sure you've got the right one is to talk to your supplier. You may also need a buffer tank with a ground source unit; again talk to the supplier.
The right cylinder-8
Hot water cylinders for use with heat pumps have been developed for that specific use. They must have very large heat exchanger surface areas and the coil must be positioned low down in the vessel.
Tank capacity tends to be relatively large because for every 1kW of output from the heat pump 0.3m2 of surface area is required. Also, you must take into account summer operating conditions for example A+20 @ W50 (A = air temperature, W = desired water temperature) as the heat output of an air source unit will increase in the summer.
Other renewables-9
If you want to use solar collectors for hot water and provide space heating support to a heat pump, you need to decide where best to place the solar collectors.
It's not just a case of putting them on a south-facing roof and hoping for the best. Their performance will be affected by the angle at which they are placed. So, rather than having a gentle angle so they work at their best in the height of the summer, consider changing it to optimise their collection capacity to when the sun is lower in the sky in the winter months. That way, when there is greater heating demand, the support of the heat pump by the solar system will be most effective.
If in doubt,ask!-10
Manufacturers and suppliers know what they are talking about. Don't be afraid to ask and get good technical advice from them.
For further advice contact MHS Boilers at www.mhsboilers.com