Any competent builder or plumber can install a ground source heat pump. The process is simple, especially with Kensa’s help. Whether you’re upskilling or in need of a heat pump refresher, run through our step-by-step guide to installing a ground source heat pump.
Calculate the property’s heat load
Arguably, the first part of planning a ground source heat pump installation is the most important – calculating the property’s heat load. To do this, you need two vital bits of information: the peak heating load in kilowatts (kW) and the annual heating load in kilowatt-hours (kWh). Remember that Kensa can support you with all elements of design.
If the building is being upgraded in insulation at the same time, it is perfectly fine to factor this upgrade work into the heat loss calculations, but it is equally important to ensure that the planned work is completed. If the heat pump is also supplying domestic hot water then this load also needs to be calculated and added to the numbers.
Figure out the heat losses: room by room
While the ground source heat pump itself will most likely be a single unit with a stated kW output, each room in the building is going to have a different heat demand, so it needs its heat emitter – such as radiators or underfloor heating – to be individually calculated to meet that heat demand.
When using a heat pump instead of a boiler, the rule is always to size the emitter so that it is capable of heating the room using the lowest possible water temperature, as this maximises energy efficiency.
Practical limits for radiator sizes usually mean getting below 45°C flow temperature is rare, but underfloor heating can sometimes work as low as 30°C. The usual practice is to work out which room needs the highest water temperature due to practical limits and then size all the other emitters to the same temperature.
Select the heat pump
Once you know the peak heating load and heating flow temperatures, a suitable heat pump model can be selected. You can determine the efficiency (also called Coefficient of Performance or CoP) of that heat pump at the heating water temperature by referring to the manufacturer’s technical data. For example, here is our technical data for the Evo ground source heat pump.
Determine the size of the ground array
The efficiency rating combined with the annual kWh demand of the building will determine the size of the ground array. One of the ironies of using the newer generation ultra-efficient heat pumps, like the Kensa Evo, is that a higher percentage of the total heat output comes from the ground, not the electrical input – meaning that ground array sizing has to increase slightly.
The ground array design and the installation can be supported by your manufacturer or an experienced installer – we at Kensa can certainly help with the design. The Microgeneration Certification Scheme (MCS) does provide design guidance or specialist subcontractors, such as Kensa Contracting, exist to do this work – especially for larger projects.
If you’re working on a new build or renovation and a digger is already on site, that’s the perfect time to install the ground array. For retrofits, we can recommend groundwork contractors to the end user, ready for the installation of the ground arrays.
It’s important to remember that the initial heat losses must be accurate, as the ground array design cannot cope with inaccurate load calculations.
Plumb up & purge the system
Ground source heat pumps have two separate wet systems with no connection between them. Flow rates and the sizes of pipes used in the plumbing are very important, with one of the most common faults being low flow rates. Installers should know how to use a pipe sizing nomogram and calculate pressure drops in a system.
The design of both the ground array manifolding and heating distribution system should aim for even distribution and high flow rates. You should use Tichelmann, also known as ‘reverse return’ plumbing designs, on both systems if practically possible. Pipe sizes will usually be one size larger than typically expected on a boiler system in a similar-sized property. Apart from this, standard good practice in plumbing is all that you need to know.
Ground arrays are invariably filled with an antifreeze and water mixture. Filling and purging require a separate pump and container; this is just about the only special tool you need to install a ground source heat pump. This antifreeze mixture must be circulated through the heat pump ground side before power is ever applied to it – it’s just about impossible to damage a ground source heat pump, except by running it without antifreeze.
Get the hot water flowing
Hot water systems are usually very similar to a common Y-plan design with a separate hot water cylinder, although the 3-port valve will not have a mid-position in operation.
Getting good domestic hot water performance relies on having matched components. The internal diameter of the coil within a cylinder affects the flow rate; this is just as important as getting the surface area of the coil right.
Thermal stores can be very difficult to set up and get working well with a heat pump, which is mostly due to the lower operating temperature compared to a boiler. The simple solution is to use a cylinder approved by the ground source heat pump manufacturer.
Some systems will need a separate smaller storage tank known as a buffer tank. You can often avoid this by using a few open zones and ample pipe sizes. The heat pump manufacturer should again be able to provide you with guidance on the minimum flow rates and the minimum volume of water in the circuit, but don’t be tempted to try and use a thermal store to provide buffering.
Choose the right controls for your customer
Heat pumps can be controlled by any means the end user wants; at the end of the day it is just a box that makes hot water on demand. Unfortunately, some manufacturers like to complicate things and try to have the building controlled by the heating appliance; in our opinion, it should always be set up the other way around.
The ground source heat pump will operate trouble-free for 25 years, as will simple room thermostats.
Commission the heat pump
Setting a new system to work shouldn’t be complex and doesn’t require a specialist to attend. If good plumbing practice has been followed, all the air bled out, systems carefully filled and valves opened, the heat pump should start right away and give full heat output within a couple of minutes.
It will usually take longer for the building to warm up than with a boiler, but only because most boilers are oversized compared to the true heat load – not because heat pumps take time to settle in or any other urban myths.