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I have a 2 bedroom condo that I pay for hot water and wonder if this would be a green choice that makes sense. Usually 3-5 people taking showers and dishwasher and clothes washer. Electric is expensive. Does anyone have any experience with these units?
Typically, an AC unit extracts heat from inside air and exhausts it to the outside air....These clever guys run pipes thru the exhaust to warm water....Good idea. Why waste the heat produced?
Their numbers work out right-- They claim to extract ~ 2700 BTU/hr, (65,000/d) and it takes ~ 54,000 BTU to warm 100 gal of 60* source water to 125*....
The problem is, that would mean your AC unit would have to be running continuously 24hr/d....365d/yr.... to keep you in hot water
....and is 100 gal day enough for 3-5 people ? ... Usually a figure of 80-100 gal per day per person is used to design plumbing capacity.
This unit may put you in more hot water than you think. Think twice.
I'm an energy engineer and get asked this pretty often. As most energy questions, the answer is "It Depends".
DESCRIPTION:
The standard generic installation is a HVAC "Split-System" with a unit outside and a unit inside, and two pipes run between them.
A "heat-recovery" system is the above, but there are some additional piping and valves in the outside unit, and piping run inside, to a water tank holding your drinking hot water.
When the A/C runs, it has to reject it's heat, and that's normally done with the outside unit's coils and fan, but the heat-recovery unit first uses it's extra piping to heat the indoor water tank.
Other Concerns:
Cost of the fuel saved; cost of the additional equipment installed, cost of the additional maintenance needed; years you expect to stay at that location, fuel cost escalations.
The one that usually kills the idea is you will still have the cost of the heater needed for when the A/C isn't running and generating that extra heat.
The generic typical worst case problem: You don't run the A/C in the winter when you need the most hot water. So you still need to purchase, maintain, and fuel the water heating hardware. You end up with a significant additional first cost of the equipment, plus a small additional maintenance costs.
All the above usually means the pay-back years to have this additional capability is typically too long for most owners. The common exception for this would be those who have gone off-grid, where they have no natural gas, or grid-electricity, and any electricity saved is very helpful.
The problem is, that would mean your AC unit would have to be running continuously 24hr/d....365d/yr.... to keep you in hot water
....and is 100 gal day enough for 3-5 people ? ... Usually a figure of 80-100 gal per day per person is used to design plumbing capacity.
This unit may put you in more hot water than you think. Think twice.
This is in Honolulu so 24/7, 365 days AC a year would be no problem. But because electricity is so expensive at $.35 per kwh and growing most people don't run their AC that much. The thought is that if I eliminate the cost to heat water by getting the comfort of AC more often would it make sense. The hot water is needed, the AC would just be a benefit.
Have you thought about a passive solar roof top water heater ? Can be either factory built or home built using black plastic pipe in a frame made of used lumber. Sunshine is free energy.
Have you thought about a passive solar roof top water heater ? Can be either factory built or home built using black plastic pipe in a frame made of used lumber. Sunshine is free energy.
This is a condo so passive solar is out. I do have a condo that installed passive solar about 50 years ago. It is still running and actually was so over engineered that as collectors have failed we are just bypassing them. We have replaced our storage tank and will have to replace collectors at some point but this has been a money saver for decades.
I'm an energy engineer and get asked this pretty often. As most energy questions, the answer is "It Depends".
DESCRIPTION:
The standard generic installation is a HVAC "Split-System" with a unit outside and a unit inside, and two pipes run between them.
A "heat-recovery" system is the above, but there are some additional piping and valves in the outside unit, and piping run inside, to a water tank holding your drinking hot water.
When the A/C runs, it has to reject it's heat, and that's normally done with the outside unit's coils and fan, but the heat-recovery unit first uses it's extra piping to heat the indoor water tank.
Other Concerns:
Cost of the fuel saved; cost of the additional equipment installed, cost of the additional maintenance needed; years you expect to stay at that location, fuel cost escalations.
The one that usually kills the idea is you will still have the cost of the heater needed for when the A/C isn't running and generating that extra heat.
The generic typical worst case problem: You don't run the A/C in the winter when you need the most hot water. So you still need to purchase, maintain, and fuel the water heating hardware. You end up with a significant additional first cost of the equipment, plus a small additional maintenance costs.
All the above usually means the pay-back years to have this additional capability is typically too long for most owners. The common exception for this would be those who have gone off-grid, where they have no natural gas, or grid-electricity, and any electricity saved is very helpful.
This is Honolulu and electricity cost about $.35 per kwh. The use is about 1000-1400 per month. I will be installing a split system replacing window units and a new HW tank soon so the additional expenses don't seem so large. The distance from condenser to storage tank is less than 12 feet.
I am paying to heat water no matter what. The tenants run the AC a limited amount because of the cost. I actually am looking at does it make sense to use AC to heat water. The hot water is needed, the AC would be a benefit of heating water.
I do have a condo that has a ground source heat pump to heat our water and the AC from this is ducted into out garbage room. Seems a waste but our lobbies are all open air so there was really no place to utilize this.
By the time you get done paying for the modifications (and potentially damaging your AC or voiding the warranty) you might as well have paid the water utility.
This is in Honolulu so 24/7, 365 days AC a year would be no problem. But because electricity is so expensive at $.35 per kwh and growing most people don't run their AC that much. The thought is that if I eliminate the cost to heat water by getting the comfort of AC more often would it make sense. The hot water is needed, the AC would just be a benefit.
The 80 gallon units work great for med-size families.
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