The False Economy of a ‘Cheap’ Heat Pump.
When is a heat pump not a heat pump?
Arguably, when the ‘heat pump’ is a converted air conditioning unit.
An air conditioning unit and a heat pump are very similar technologies. They are heat exchangers where the air conditioning unit is converting warm air to cold, and a heat pump is doing the opposite. Does that mean that a converted air conditioning unit makes a good heat pump? Unfortunately, not necessarily.
When you cool a house in this country, you might require a supply of air at 15 degrees when outside it is 30 degrees. That is a differential of 15 degrees. Likewise, you might require a heat supply of 30 degrees inside to maintain a comfortable temperature when outside is freezing or below. That is a differential of 30 degrees plus. The components in a unit therefore need to work much harder to heat a property than they do to cool one. The vast majority of converted air conditioning units, in consequence, use far more energy to achieve desired temperatures than they are designed for. This causes fatigue and results in significantly shorter life expectation than units designed and built as heaters, not coolers.
Why are so many heat pumps installed in the UK converted air conditioning units?
Like so many things, much comes down to price. Firstly, the units are generally smaller than the alternative. They often having evaporation fins spaced closer together, for example, which is standard in an air conditioning unit. Smaller units are more economic to ship and install, and the size obviously benefits the home owner too. Also, air conditioning units are manufactured in far larger quantities than heat pumps, currently. It is cheaper to use components which are already mass produced, driving down the cost of the entire unit.
What is the alternative?
Heat pumps which have actually been designed to heat, not cool, often come from colder EU countries. These countries have been using and refining this technology for decades – it is not the new kid on the block for them.
They generally come with solid, aluminium or stainless steel panels which do not rust in humid climates. The heat invertors are high quality, built to withstand the rigorous demands of a cold winter. Electrical and control compartments come dust and water sealed, while components remain easily accessible for maintenance and replacement as needed.
It is unusual to get these necessary design features in the cheaper, converted air conditioning units. In addition, the wider spaced evaporator fins are less likely to freeze up on colder days. When the fins are closer together (less than 2mm apart) the defrosting cycle is employed far more frequently. This is both costly and increases thermal fatigue, again reducing the life span of the unit.
Why is a purpose built heat pump more expensive?
Obviously, quality comes at a price. The design features listed above are more costly to produce and fewer of them are manufactured. Often, these units are larger in order to accommodate design features which makes them more expensive to ship.
However, a purpose built heat pump in a well designed heating system can significantly reduce your heating bills when compared to gas or oil. Much of this is down to the efficiency of evaporators and invertors which have been designed to resist thermal fatigue. With regular maintenance, repairs will be few and life expectation in the region of 15 years plus.
The cheaper alternative, however, may increase your heating bill. The pump is likely to have to work a lot harder, not having been designed for purpose. This decreases energy efficiency. The life expectation of a converted air conditioning unit is considerably shorter, possibly up to 10 years. Even this is achievable only if it has been designed and installed well.
‘Designed and Installed well’, surely, that’s a given?
Unfortunately, this is another very harsh lesson with cheaper, converted air conditioning unit heat pumps. The unit itself is simply a source of heat and is not a heating system. It needs to be installed with many other parts to get the heat inside your house, and for you to be able to control it.
When buying a cheaper heat pump, you are nearly always simply buying the pump itself. In contrast, when you purchase a heat pump from Stiebel Eltron for example, you are not just getting the pump itself. You are also buying the buffer tank, cylinder, safety kit, circulating pump, controller, internet service gateway and remote controller. They provide the whole system as a package as standard.
Furthermore, with a converted air conditioning unit, the liability for any issues is often disputed between the manufacturer and the installer. This is because the installer ends up sourcing and designing the remainder of the system. You need to make sure who is taking responsibility for any niggles, and that your warranty is valid. This makes your choice of installer massively important too. It is also vital as you stand to incur significant costs to your heating bill if calculations have been done incorrectly or inexpertly. Always ensure your installer is experienced and qualified.
What constitutes value in a heat pump?
To truly work out the value of a heat pump, ensure you are considering the cost of the entire heating system, not just the pump itself.
Ensure your heat pump is the correct size for your property to enable maximum efficiency. You want to save money on your heating bills and reduce environmental impact. Do not rely on COP or SPF, which are values supplied by manufacturers to illustrate the efficiency of their heat pumps. These can be wildly misleading and there is a lot of leeway in the regulations as to how these figures can be produced. An experience installer needs to calculate the correct heat pump size specifically for your property.
Do not underestimate peace of mind. Be satisfied that your system is well designed and installed. That it will need few repairs and last you many years. Ensure it can be accessed and maintained. Most importantly, be sure it will save you money over time and reduce your carbon footprint.
Overall, as with all things, there are of course advantages in a cheaper option. At PBT Installations, we are firm believers that your decision should be an informed one and we are happy to discuss all options with our customers / potential customers.