32 THE CLIMATE CHALLENGE


Addressing a common misconception on heat pump-led networks


Ed Morris of Altecnic tackles a common assumption around heat networks incorporating heat pumps, in terms of whether interface units can be installed to deliver on demand and efficiency.


T


he assumption is as follows: “It is a heat pump led network therefore the flow temperature is low, and I can’t use instantaneous heat interface units (HIUs) as I won’t get enough direct hot water  output. o,  will have to utilise DHW stores within the apartment to meet my DHW demand.”


DOES A ‘LOW FLOW’ NETWORK RULE OUT INSTANTANEOUS HIUS? HIUs that have DHW plate heat exchangers that are specifically designed for low primary side temperatures can give very high DHW outputs and primary return temperatures. Current market leading HIUs can output 44 kW of DHW at a 55°C primary return temperature. CIBSE’s CP1 (2020) gives guidance stating that even three bed apartments, with two bathrooms only require 35 kW of , so the s currently available to engineers are efficient enough to be fitted on numerous networks.


ropping the primary flow temperature


further, down to  gives an output of .  with  at , covering the requirements of most single bathroom apartments. owever, should you reuire more output, some s available have the option for an inline electrical element to be installed and controlled by the . nder most circumstances, heating and standby, the element is not in use. owever, the moment there is a  demand, the  energises the element and boosts the primary temperature by up to 10°C. Using the example earlier in this paragraph, the  output increases to a potential 56.5 kW.


As the element is on the primary side of the , then the networ delta T is not reduced, in fact it is increased. f the electrical element was on the outlet secondary of the  or in a cylinder, then this would have a negative effect on the networ delta T. s a result, networ efficiency would be reduced, losses would increase and the potential for the building to overheat would also increase.


CIBSE’S GUIDANCE STATES THAT EVEN THREE BED APARTMENTS WITH TWO BATHROOMS ONLY REQUIRE 35 KW OF DIRECT HOT WATER


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