Overview
This article is designed to provide details of a specific installation of an air source heat pump facility, where the implementation is air-to-air rather than air-to-water. Although rarely promoted by suppliers and the UK government, air-to-air is much more cost-effective and quick to install and has been proven over many years across Europe. These kind of systems are now used in Orkney, where other options such as gas, wood burners and oil are largely unavailable or uneconomic.
A "new generation" air-to-air system is ideally suited to properties that are "all electric", i.e. rely on electricity for all their heating requirements, with no central heating system. Typically such homes are heated with electric radiators (often with night-storage devices). With current electricity prices these use huge amounts of power and can be extremely expensive to run. Furthermore, their heat output is poor in the late afternoons and evenings. Air-to-air heat pump system systems are also suitable for homes that already have another form of heating (e.g. gas or oil-fired CH systems), but find these can also be very costly to run and may benefit from augmentation with an air-to-air system. Finally, air-to-air is ideal for new builds and occasional occupancy properties, as they provide almost instant heat in a very efficient manner.
How it Works
There are just two elements to an air-to-air heat pump system: an external unit that extracts heat from the air (down to a temperature as low as -10C to -15C) and uses this to heat a fluid to c.90C that is then pumped (when needed) to internal devices that look exactly like air conditioning units. Both internal and external units are almost silent. Photographs of an external unit and internal unit are provided above. The internal units are "smart" and typically controlled by an app (and/or remote controller) that handles the hour-by-hour temperature that you want the room to be heated to. For the system I have had installed there are two internal units and one fairly small external unit. The internal units are powered from the external unit, and each has a pair of small flexible pipes to them (so each has 3 connections - 1 power and signalling, and a to-pipe and a from-pipe for the fluid flow). With our two units that is 6 connections in total, but all are small and hidden in moulded ducting (obtained from ManoMano, see image below) - the external unit only requires a fairly small hole through the outside wall of the house for these connections and the power connection. Installation of the units took place over two days, and disruption was minimal.
Power consumption and cost
The total cost of the installed system was a little over GBP5000 (0% VAT rated), plus the electrical installation - we used the circuit from one of our now redundant storage radiators for the link to the external unit, which was completed a few days prior to the system installation and took roughly 3 hours.
Each internal unit in my system is set to provide 20C during the day and 17C at night. These settings can be dynamically changed via the app, and their power usage is monitored at all times. In theory they provide roughly 5:1 efficiency, i.e. for every 1kWh used a total of 5KWh of heat is provided - this is for the latest technology from Daikin (see linked PDF brochure Daikin_New_Multi.pdf). Other providers such as Panasonic, Vaillant etc., have similar systems. The power usage can be viewed on a per hour, day, week and year basis, so it is possible to check the actual power usage, and hence cost, of running these systems. In my case the system was installed in late January, and since then has provided consistent heat for two large areas of the house.
The power usage has averaged 4.5kWh/day (January to March) and less than 2kWh/day in April - assuming peak rate charges at the current "standard" rate, i.e. c.34.5p/unit (although I pay less than this on a contract that expires in late August 2023) the higher level of usage equates to an average daily cost of GBP1.55/day - assuming it is actually in use (drawing power) at the higher level for 200 days/year, this amounts to just GBP310/year - i.e. exceptional value compared to other alternatives. Some observations regarding the usage should be made: (i) we actually pay 9p at night and 19p during the day for electricity, so the running cost is much lower at present; (ii) we still have some night-storage radiators running, but have turned off three completely and set the others on lower power settings; (iii) our property is quite well-insulated, but does have a lot of glazing, including three sets of french doors and two windows in the main room downstairs; (iv) at night we like to use our wood burner, which augments the evening heat and looks nice!; (iv) the system has a small annual maintenance cost, much as a conventional CH system would have; (v) this does not provide a solution to water heating; (vi) for some reason there is no separate government support for this kind of installation, but as it so much cheaper and less disruptive than "wet" systems, this should not be a major factor when deciding on whether such a system is worth installing.
With other measures to reduce our annual electricty usage (e.g. using LED lighting everywhere, moving to more efficient/low power devices, doubling insulation in the loft area using 100mm rolls of wool insulation) it will not be until this time next year that the full value of this and other measures can be calculated, but initial results suggest that overall usage in kWh is already around 33% less when compared to 2019/20 and this is probably a considerable underestimate of the reduction achieved.
