I've seen too many dual-temperature water coolers (i.e. that dispense cold and hot water) that have condensers on the back from the cool water, and they use a separate heater for the hot water. Why not simply wrap the hot water reservoir with the condenser coils, therefore re-using the heat energy from the cool water?
-- devnull, Jul 20 2008

Heat Exchanger thermodynamics http://web.mit.edu/.../notes/node131.html
If you look at the formulas, the rate of heat exchange (Q{dot}) is lower for lower Delta T. Since a condensor in this case will only reach about 40 °C, heating will be very slow. Additionally, around those temperatures, and with the long heating times, you're creating the ideal circumstances for legionella to thrive. [sdk16420, Sep 25 2014]

This could probably go as a separate idea, but there are so many instances where hot/cold energy could be used more efficiently. At my gym, pump cold air in to the gym, yet separate heaters heating the water

+1
-- g00r, Jul 20 2008


your idea makes me think of the people who realized that putting the motor on top of the fridge saved a bunch of energy compared to putting it under the fridge ...where it warmed up the fridge

motor on top fridges remain rare as a result of tipping hazard; maybe they could have ductwork like Ben Franklin thought of
-- beanangel, Jul 21 2008


Great idea +1
-- nomadic_wonderer, Jul 21 2008


Isn't there a rule of thermodynamics or some such, which says that cool things and hot things near each other attempt to reach each other in temperature?

If this is true (and forgive me, for I am no more a scientist than a bakery expert) then you'd have two new problems: one, to stop the hot water transferring all its heat to the condenser and thus cooling down, and two, to stop the condenser getting hotter from the hot water, and thus heating up (which it's not supposed to do cos it's supposed to carry excess heat away from the cold, not add to it).

Or something. Anyway, if you end up having to re-heat the hot water and re- cool the cool water then surely there's some loss of energy somewhere, or at least not any gain...
-- cheesecake, Jul 22 2008


Not a bad summary, [cheesecake].
The Devil is in the Detail.
-- gnomethang, Jul 22 2008


//motor on top fridges remain rare as a result of tipping hazard//

Which is kind of a shame, because the tipping hazard could be overcome with a 50-cent bracket.
-- nomocrow, Jul 22 2008


// Isn't there a rule of thermodynamics or some such, which says that cool things and hot things near each other attempt to reach each other in temperature? //

The Zeroth Law, maybe? If the condenser and the hot water reservoir are touching, they will reach an equilibrium (??speling), and their temperature will be equal. If anything, this will reduce work on the heater if it must be installed to produce a *hot* hot water temperature, and reduce the work on the condenser, if it must be installed to completely condense the refrigerant.
-- devnull, Jul 23 2008


This is actually a very good idea, thermodynamics wise, but I think the isue would be one of scale. The compressor runs only when the cold water needs cooling, running it when the hot water needs heating could lead to freezing the cold water, or, conversely, when a lot of cold water is needed, it might boil the hot water side.
-- cblunds, Jul 23 2008


//when the hot water needs heating could lead to freezing the cold water//

Rainy Day + Reverse Cycle Air Conditioner = Ice

Probably best used as a system to increase efficiency, rather than to replace the current system totally [+]
-- xxobot, Jul 24 2008



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