Heat distribution and operation
Heat pumps are recommended for installation in heating systems where big heating surfaces are to be heated by low temperature heating water. Heat pumps can generally produce heating water with high efficiency up to maximum 44-46 °C. In this case the flow temperature has to be designed for 42–43°C maximum taking into consideration that there is a mixture of hot water and colder return flow in the buffer tank. High yearly COP values, or Seasonal Performance Factors can be reached only in this case and this will lead to low operational costs. The recommended temperature differentiels in heating mode max. 43/38°C, in active cooling mode 7/12 °C (in case of fan-coils). In case of surface cooling (for example, ceiling or wall-cooling) or if the whole contruction is cooled, only higher temperatures of cooling water can be employed, otherwise vapor will condense on the surfaces.
When evaluating COPs of different heat pumps, it must be taken into consideration that the COP changes every moment during the operation of the heat pump (in winter time when the outside temperature is very low, the COP can fall down to 2.5-2.8-ra, but if the heat request is less, the COP can increase up to 6.0). In addition, the flow temperature has a very serious impact on the COP (for example, at 35 °C of flow temperature the COP is much higher than at 40-45 °C). We recommend to aim at seasonal COP= 4.0.
Generally saying, to have serious savings on operation, the heat pumps must run (of course we speak about perfectly designed systems and not about undersized ones!) as much as possible all over the year. In practice this means that we recommend to design heat pump systems in traditional building both for heating and cooling since heat pump systems have higher efficiency in cooling mode than the air-cinditioners or liquid chillers. Heat pump systems designed for heating only, can be operatid with high efficiency in assets that are heated all over the year (for example, in community or private indoor swimming pools where the heating water is produced at about 35°C which is ideal for heat pumps).
