Heat Pump Myths

Geothermique Ltd

Renewable Energy Solutions from the Experts

Geothermique Ltd.



Heat Pump Myths Myth 1: Heat pumps require larger radiators than Condensing Boilers. Condensing boilers require a flow and return temperature 60 deg C and 40 deg C giving an mean water flow (MWT) temperature of 50 deg C. Heat pumps can operate with a flow temperature of 55 deg and a return temperature of 50 deg C giving a mean water flow temperature of 52.5 deg C. This actually means that larger radiators are needed for condensing boilers. Unfortunately few installers of gas and oil boilers will upgrade radiators when changing from non condensing boiler to a condensing boiler. We recommend that heat pump systems are designed for as low a flow temperature as practical . Myth 2: Older poorly insulated properties are not suitable for heat pumps. Heat pumps care not about the insulation in the building, their efficiency is simply determined by the flow temperature they operate. This means that provided radiators are correctly sized, heat pumps in poorly insulated properties will operate with the same efficiency as those in new properties. Myth 3 Heat pumps are not suitable for microbore distribution systems. Microbore systems use a manifold distribution system with all radiators fed from a centralised location. The pressure drop calculated for 10m of 10mm copper pipe using a 25 % antifreeze feeding a 1kW radiator is about 9 kPa . The typical pressure drop in the plate heat exchanger of a heat pump is about 20 to 25kPa, We then also need to add pressure drops from pump unions, flow and return pipes and filters. A pressure drop of 9 kPa is perfectly acceptable and represents only a small portion of the total pressure drop. Comparing the pressure drop calculated using a standard distribution system using 22mm feeding 6 similar radiators we would see a pressure from of 7.5kPa to the final branch point. Comparing microbore to a standard piping arrangement we see only a difference of about 1.5 kPa. We have assumed that the index loop is on the final radiator circuit. Note that a 1kW radiator is equivalent to 2m long 600mm high Stelrad K series radiator operated with a MWT 50 degC. In summary we think that microbore distributions are generally acceptable. In situations where there is a long run from the manifold to radiator position with a very radiator a detailed pressure drop calculation may be required.