Heat pumps - operational considerations
Regarding the technical and administrative aspects of operation, there are important differences between green space heat schemes and the typical incumbent – or business-as-usual – technologies. However, heat pump operational requirements are not onerous or expensive, and administrative costs are mostly only incurred when there is a revenue stream (subsidy or heat sales) to manage.
Heat pump plant
Heat pumps operate on very different principles to the incumbent heat generation technologies (mostly gas boilers, but also oil and LPG boilers). The practical features of heat pumps necessitate some differences in treatment, but if designed and operated correctly the user experience should be comparable in terms of comfort and the effort required to keep the system running as it should.
Issues for building users
When a heat pump system is installed, the designer must check that the heating distribution systems of the building(s) that it serves are adequately sized so that the new system will be able to provide a comfortable inside temperature during the coldest weather. In the case of retrofits, sometimes this will mean the installation of larger radiators or underfloor heating. However, even when the heating distribution system capacity is adequate, rooms heated by heat pump-fed radiators are typically slower to warm up when the heating is first turned on. This means that heating timers may need to be adjusted so that the heating turns on 0.5 to 1 hour earlier than would have been required with a fossil fuel boiler-heated system.
Ground and water source heat pumps are typically louder than the quietest available gas boilers, but quieter than the noisiest gas boilers (particularly older models). By siting the heat pump unit suitably and installing noise attenuation measures where appropriate, the noise emissions from ground and water source heat pumps will be acceptable to building users in most contexts.
Once a heat pump system is commissioned and optimum settings have been found for the various elements of the heating system, the need for ongoing adjustments will rarely arise. Heat pump controls are typically as good as, or better than, the controls on a system heated by a fuelled boiler.
Issues for building owners or responsible operators
There are a few routine tasks and checks that those responsible for building services are advised to carry out on heat pump plant, but these are fairly simple and quick.
As is the case with a fossil fuel-heated system, visual checks of the pressure gauge on the heating distribution outlet should be made in order to ensure that the system is operating within range, and the circuit may need to be bled and/or topped up via the filling valve from time to time. For a ground or water source heat pump system, similar checks and maintenance actions will also need to be carried out on the ground loop.
Filters on the ground loop and/or heating distribution side of the heat pump require periodic checking and cleaning. Where a new heat pump is connected to an older heating system, checking and possible cleaning will need to be done every 1-2 months initially but less frequently (eventually once per year) as the contaminants are gradually removed from the system. This task can be performed with basic tools by following instructions in the heat pump’s manual.
Most heat pump systems that deliver hot water as well as space heating are designed to periodically and automatically over-heat their hot water tanks to control legionella bacteria.
Installations are also designed with various shutoff mechanisms that are activated in the case of faults or leaks.
Servicing and repairs
Heat pump units are typically provided with warranties of 5 or 7 years, normally conditional on the unit having been serviced annually. Some heat pump manufacturers and installers offer annual servicing. The servicing must be carried out by an ‘F’ Gas certified engineer due to the presence of the refrigerant in the heat pump.
With few moving parts and none of the stresses placed on components due to combustion, heat pumps can operate for many years without requiring repairs.
Ground heat collectors
As passive equipment subject to benign operating conditions, closed-loop ground heat collectors do not present any routine operational or maintenance requirements. (A drop in ground loop pressure would be observed during checks of the pressure gauge on the ground loop side of the heat pump.)
The presence of ground heat collectors may have implications for the use of land and future construction activities. The slight cooling of the soil relative to its undisturbed state influences the germination and growth rate of plants which grow in that soil. It has been reported that springtime germination can be delayed by around 2 weeks.
Major excavations and groundworks being undertaken in the future must take the presence of the heat collector infrastructure into account. During installation, labels are placed above pipes to warn anyone digging above them at a later date, similar to other utilities.
Water source heat collectors
Closed-loop water source heat collectors do require very occasional maintenance, namely cleaning of the heat exchangers or immersed pipes to ensure good thermal transfer (perhaps every few years) and checks to the anchoring/tethering systems (frequency dependent on exposure to rough water or other risk factors).
In water bodies used for swimming, boating or other water-sports, floating barriers to discourage water users from accessing area around the heat collectors can be installed to promote safety.
The presence of water source heat collectors will have an impact on the water temperature in a lake or downstream of a heat collector installed in a river. The scale of this impact depends on the size of the heat pump system relative to the size or flow-rate of the water body, and may be negligible. However, where a more significant impact exists, this may have implications for other users of the water body or for ecology.
Administration
If the business model under which the greenspace heat scheme is being operated involves the receipt of subsidy revenue or the sale of heat to third-party customers (or across departments/ divisions of an individual organisation), there may be administrative demands. Responsibility for the submission of periodic meter readings and other information in order to claim subsidy payments may need to be assigned and time budgeted; likewise, the preparation and amending of heat supply contracts, the issuing of bills and the resolution of issues between customer and heat seller will require time and responsibility to be allocated. Further administrative effort may be required for system performance monitoring, evaluation and issue resolution.