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NC-2009 EAc4:Enhanced Refrigerant Management

Calculation of Rc in 4-pipe air-source heat pumps

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Ricardo Sá
Director of Sustainability
Edifícios Saudáveis Consultores (503 910 767)
LEEDuser Basic Member
79 thumbs up

I have a project with an air-source heat pump that can either do heating, cooling or simultaneous heating and cooling (4 pipes).

When calculating Rc, if only the cooling capacity is taken into account, this type of equipament will be unfairly penalized. This can easily be demonstrated if compared with a situation where dedicated air-source heat pumps are installed for heating and cooling only (2 pipes), because in this situation it is obvious that the heating capacity must be considered in order to calculate Rc.

Our suggestion is to calculate Rc by dividing the total refrigerant charge by the sum of cooling capacity and corrected heating capacity (evaporator themal capacity when the units is operating in heating mode).

Do you agree with this approach?

Thanks!

 

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Ben Stanley
Senior Sustainability Manager
WSP - Built Ecology
LEEDuser Expert
188 thumbs up

Tue, 01/16/2018 - 23:04

Hi Pedro,  My suspicion is that your approach wouldn't be accepted but I don't know enough about your system design to say definitively. When the system is running in simultaneous heating and cooling, is the total capacity of the system somehow higher than the cooling capacity of the heat pump?
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Ricardo Sá
Director of Sustainability
Edifícios Saudáveis Consultores (503 910 767)
LEEDuser Basic Member
79 thumbs up

Wed, 01/17/2018 - 18:11

Thanks Ben! Yes, when system is running in simultaneous heating and cooling the useful heat corresponds to the sum of evaporator and condenser heat. Now, let me try to rephrase the question: if an air-to-water heat pump (heating only) is used how shall the Rc be calculated?
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Ben Stanley
Senior Sustainability Manager
WSP - Built Ecology
LEEDuser Expert
188 thumbs up

Fri, 01/19/2018 - 18:23

To your question, in its simplest form, the Rc should be calculated based on the total refrigerant in the system and the capacity of the system. If you're saying that the equipment capacity is associated with simultaneous heating and cooling, rather than peak cooling or heating, you might be able to demonstrate that with engineering calculations and make the case to use that value for capacity in the Rc calculation. I've never seen that done before and would be interested in what others have to say about this situation.

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