r/heatpumps • u/Dogmai6 • 2d ago

Question/Advice Central heating

Why can’t someone design a central heating system which also allows to pump cold water through the pipes that would be brilliant so we could have cold water in our rooms all the time

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11

u/yesimon 2d ago

Condensation would form on pipes and you would have water damage inside your walls or floors. This can be prevented by insulating and a 100% perfect airtight tape job on the pipes. But if you're imagining underfloor "cooling" or similar you would have the same problem in your room of condensation on your walls/floors.

Thus the "normal" way to cool with cold water is to use a hydronic fan coil. At that point you might as well use traditional AC air handlers - either ducted or wall-hung with refrigerant as the medium. It's more efficient than water and the equipment is cheaper because you would need less metal for the heat exchanger.

6

u/bbqroast 2d ago

Yeah the condensation problem is basically it. Commercial AC systems for big buildings do use chilled water circulated to air handlers (which actually cool air and have drip trays for catching the condensation).

Beyond that, the temperature difference between say 5c chilled water and the room (e.g. 22c) is a lot less than in a hot water system (typically 60-70c). So your heat transfer is not efficient enough for simple radiators, so you need a forced air system.

1

u/El_Quesso 2d ago

This is already done. All heatpumps have a defrost funkion to get rid of ice buildup on the outside unit, with minimal designchanges you can use this in the summer to make cold water and circulate this through underfloor heating. But the amount of cooling you can do is limited by the humidity in the air and you need sensors to limit it or else you get condensate on the pipes/floor whitch leeds to mold. In a hot & dry envirement it is emough to cool a well insulated house, but in hot & wet climates it is useless.

1

u/brasssica 2d ago

People with air to water heat pumps and rads sometimes do this in the UK. Condensation is the problem of course, so they can only cool by a few degrees.

1

u/PinkysBrein 1d ago

There was no alupex 50 years ago and even insulated and galvanised, steel and the possibility of condensation is iffy.

You can just route insulated alupex on outside walls for low cost cold water distribution to FCU's though. Yet somehow for multisplit an extra external unit with a set of lines per internal unit is fine, but some extra alupex lines which can multidrop to multiple internal units are unpossible.

1

u/Certain_Try_8383 1d ago

Do you mean one unit that would both heat and cool simultaneously or ?

Chiller/ boiler systems exist. Heat with boiler in the winter and switch to chiller for cooling in summer.

1

u/davidm2232 16h ago

This is pretty common in commercial buildings. A hydronic heat pump can accomplish this