A more efficient and cheaper to run home cooling system

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A more efficient and cheaper to run home cooling system

Postby bmn123 » Sun Mar 11, 2012 3:20 pm

Here are some thoughts I've had for a while, I'm after comments or shooting down if the idea is foolish.

Water stores energy well, so well that 1,000 litres of water store 1.17kwh per degree.

Night off peak energy costs are half day prices.

Refrigeration systems are more efficient with a lower temperature delta between evaporator and condenser.

Why don't we cool an insulated water storage container with the cheapest electricity at the most efficient time when the outdoor air temp is the lowest, resulting in the most efficient operation?

Then during the day, using a low power water pump, pump the cooled water into a heat transfer unit and use the stored cool energy to cool the living area.

This same system can be used with rooftop solar water/swimming pool heating pipes to achieve the following:
- Heating in winter
- Cooling without using the refrigerative heat pump when the day to night temperature difference is large. At night time, pump the warm water to the roof to radiate the heat away.

Am I on a winner or wasting my time?
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Re: A more efficient and cheaper to run home cooling system

Postby Gordon-Loomberah » Sun Mar 11, 2012 6:35 pm

bmn123 wrote:Then during the day, using a low power water pump, pump the cooled water into a heat transfer unit and use the stored cool energy to cool the living area.


Condensation could be a problem, you need to dry the air, or at least have some way of dealing with the moisture condensing out on the cold surfaces. The cooled water heat exchanger only has to be at the dew point or lower for condensation to occur. Depending on where you live, that may be a minor, or a huge problem. I know I frequently see DPs of over 20C in the warmer half of the year, and I'm nowhere near the coast, which generally has higher DPs in summer/onshore wind conditions.

Several forum members, including myself, are using solar heated water in a hydronics system to heat the house in winter.
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Re: A more efficient and cheaper to run home cooling system

Postby bmn123 » Sun Mar 11, 2012 7:55 pm

Good point about the condensation. I am thinking of a repurposed split system indoor unit, instead of R12/410 in the coil, have water as the heat transfer medium.

Tell me more about the hydronics - I've just spent some time on google and every (commercial) site says solar is no good. I live in Melbourne so winters are very cold so any details of a working purely solar heating system with a few thousand litres water storage is what I'm interested in.

Thanks
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Re: A more efficient and cheaper to run home cooling system

Postby Gordon-Loomberah » Sun Mar 11, 2012 10:38 pm

There is a photo of the 78 tube hydronics array in this thread, and I've said a few things about it in other threads that should turn up in a search. I have a wood-fired stove with wetback that I'm rebuilding with new firebricks and stainless steel internals that will also be connected into this system.

alternative-building/topic2579.html?hilit=hydronics%20array#p17903

The mean winter temperatures are significantly colder here than Melbourne (by 4 or 5C), and once I have the 1000l tank and the wetback plumbed in, it should keep us warm though winter. At the moment it only has 250l of water storage and is ok when it is sunny, but that's not enough for cloudy weather.

Energy Matters has some info about solar hydronics heating here: http://www.energymatters.com.au/renewab ... hydronics/
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Re: A more efficient and cheaper to run home cooling system

Postby Tracker » Mon Mar 12, 2012 3:34 pm

.
..and you could consider a heat-pump, where the heat is extracted from the COLD tank and transferred to the HOT tank, thus gaining HOT water for normal use and cold water for later cooling..
Only problem is that if you don't use the "COLD", then there will be no capacity to draw more heat the next night..
I have never been able to come up with a system of supplementing the system.. ie.. ability to feed in more heat, if the COLD water gets too cold ( COP decreases with temp differential ), or vicky-versa..
Gordon-Loomberah wrote:Condensation could be a problem,

As with any cooling system, that would be the case -- take the normal Air-Cond, that runs like a tap in coastal climes..
..sealing the COLD storage container to prevent condensation within the insulation, rendering the insulation useless, would be the biggest pest in my thinking..
Had thought about one of those 1000Ltr cube containers consisting of a poly-tank in a steel cage, as used for printers ink etc.etc. ... Thought about getting one sprayed with Polystyrene foam, but would think that it would crack off when you filled it and the tank distorted.. Could seal the lid/tap and lightly pressurise until the foam sets and you can fill it with water..

PS - and using a phase-change medium stores even more energy, as Gordon has previously demonstrated..
The big issue with phase-change is that it is harder to deal with some materials like wax, which become pretty much an insulator, when cool..

PPS
Water stores energy well, so well that 1,000 litres of water stores 1.17kwh per degree.

So how would this work in practice..? My AirCond is rated at 12,000BTU cooling....and draws 1.2Kw of power..
To use a heat-pump reasonably efficiently (ie a fair COP) I would need to cool the water to only about 10degC..
If I wanted to use this cool water in a Split-Air-Cond inside unit, then I would need to force the cold water through the evaporator (designed pretty much for GAS), and I could extract the cold (HeHe) up to about 22degC.. That's a 12 degree change or 14KwH of "Power"...
So - how much cooling is that going to achieve.
14 kilowatt hour = 47,770 Btu
Does this suggest that all that energy would be gone in about 4 hours of equivalent normal running via Heat-Pump (RAC) -- IF you could pump the water through fast enough..?
..
.
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