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Heat Pumps Technology Guide SEAI 9. Electricity supply issues Key messages • The maximum import capacity of the incoming electrical supply to the site must be sufficient to accommodate the extra electricity demand of the heat pump system. • Peak load depends on the size of heat pump and the motor controls installed. Generally, heat pumps with a rated thermal output of more than 15 kWth will require a three-phase supply. Heat pumps are electrically powered and so any installation, including associated ancillary equipment (e.g. circulating pumps, cooling fans and defrost heaters) increases a site’s electricity supply load. That’s why it is important to make sure that the8 Maximum Import Capacity (MIC) of the incoming electrical supply is sufficient to accommodate the additional electricity demand of the heat pump system. Similarly, the site’s own internal distribution circuit(s) to which the system is to be connected must have sufficient capacity. The main electrical load in a heat pump is due to the motor that drives the compressor. At start-up, the compressor motor momentarily draws a higher current (and thus power) than in normal operational mode. This peak load depends on the size of the heat pump and the motor controls installed. The starting current of compressor motors is usually controlled by a soft starter or variable speed drive. Depending on existing loads, the site’s power factor could also be affected by a heat pump installation and may require correction. Generally, heat pumps with a rated thermal output of more than 15 kWth will require a three-phase supply. However, there are some systems available, with outputs of up to around 20 kWth and containing two heat pumps in one unit, which can automatically manage the current drawn so that a single-phase supply can be used. In marginal situations where a small increase in electrical supply capacity is required, but the cost of bringing in the extra electricity supply makes the heat pump system installation economically unviable, it may be possible to implement bespoke intelligent control of the heat pump operation to limit the maximum load. It is always necessary to discuss electricity supply with the prospective maximum import capacity heat pump supplier and the electricity distribution system operator (ESB Networks). This holds even when the Maximum Import Capacity ( and site distribution circuits appear to be adequate. It is important that the electrical loads are balanced for a three-phase motor (compressor) to run correctly. Loads on the phases must be balanced within the installation. It is important that the loads on the rest of the site are also balanced. This avoids significant differences between the phases, an important aspect, which can otherwise cause operating problems and compressor failure. The electricity tariff should be suited to the heat pump system and its operating schedule. For example, if night storage electric heaters are replaced by a heat pump system in a building that needs all of its heat during the day, then the new electricity tariff selected should take this into account. In this case, failing to change the tariff would mean unnecessarily expensive electricity. 36PDF Image | Heat Pumps Technology Guide
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