Inexpensive heat pump and A/C enhancement

[Ivan Seeking]

While in California – the land of air conditioners and swimming pools – I noticed a relatively easy freebee for air conditioners and heat pumps.

First. for comparison and perspective, consider that geothermal transfer systems are now used to replace the condenser/evaporator coil in cooling/heating systems. The ground, instead of the air, acts as the thermal reservoir for the system. Typically, [I believe that] hundreds of feet of heat conductive plastic pipe are buried on the property and then connected to the a/c unit. Since the ground is relatively cool in the summer, and relatively warm in cold weather, the system sees a smaller hill to climb for both heating and cooling; hence lower heating and cooling bills.

It seems that with very little effort, the same could be done with swimming pools. The advantage wouldn’t be as great, but the cost of installation would be much less. It seems to me that the best system would incorporate a water supply hook-up as part of the condenser/evaporator unit. A fractional HP water pump would circulate water from the pool, over the heat exchanger, and back to the pool again. The circulation pump would turn on based on ambient conditions and the water temp. In many cases, say in the heat of summer, the pool water may be as much as forty degrees cooler than the ambient temp. Generally I think this would yield the greatest advantage during the most extreme weather - during the periods with the heaviest demand for energy.

This could also elimate that noisy condenser coil fan!

Note that we often heat the pool while cooling the house anyway.

 

[Danger]

Great idea, Ivan. Now... since I've officially approved it, I expect a cut of the royalties.

 

[russ_watters]

The reason so much refrigerant piping is used in geothermal heat pumps is that the ground has to be able to not just absorb, but also dissipate the heat. Where is a swimming pool going to dissipate the heat to?

Calculations on how much heat capacity a pool has are pretty straightforward. Depending on the assumptions you use for the size of the house and pool, you'll raise the temp of the pool several degrees a day. Since it is difficult to know how fast heat can dissipate out of a swimming pool, it is tough to know whether or not this could work. Perhaps, though, an artificial water fall (ie, a cooling tower) would be able to make up the difference and keep the water cool enough.

In winter, you'll rapidly cool your pool to freezing and with a sink temperature that low, the effectiveness of a heat pump isn't all that good.

 

[Artman]

While in California – the land of air conditioners and swimming pools – I noticed a relatively easy freebee for air conditioners and heat pumps...
Note that we often heat the pool while cooling the house anyway.

This is already in existence. It is called a Desuperheater. It is basically a shell and tube heat exchanger that runs refrigerant through one side and water to be heated through the other. This water can be going to a swimming pool or to a water heater. If it is being used to preheat water to a water heater, then it is usually circulated through a holding tank that feeds the water heater when there is a draw.

With a swimming pool desuperheaters are often used with Natatorium (pool enclosure) units that both heat the water and cool and dehumidify the pool enclosure to aide in precooling the refrigerant used in the AC portion of the unit. These units usually have to have backup heatsinks, such as condensing units outdoors, this usually depends on the size of the pool.

http://www.vaportec.co.nz/products/subcdesuper.htm"
This first link shows a form of desuperheater and explains a bit about how they work.

http://www.earthenergy.ca/tech.html" This second link contains the quote below.

EE water heaters (desuperheaters) are a popular option, usually adding less than $1,000 to the total installation, but reducing the 25% of heating cost that an average household will spend on heating water for domestic use.

Desuperheaters can be "low" or "high" priority, depending on whether the homeowner wants the ground heat diverted to hot water first (thereby turning on the auxiliary electrical space heater) or to heat water only after the space heating requirement has been satisfied.

There are a number of factors that will have a major influence on the installation and performance of an Earth energy system. It is important for the potential customer to understand these issues.

 

[Ivan Seeking]

The reason so much refrigerant piping is used in geothermal heat pumps is that the ground has to be able to not just absorb, but also dissipate the heat. Where is a swimming pool going to dissipate the heat to?

We have a large surface area deep in the ground for dissipating heat - the walls and floor of the pool. A well designed pool cover for winter, and one for summer, could help as well.

Part of the practical aspect of this depends on the large load being transient. In many cases the water can also cool at night, or warm during the day.

My understanding is that heat pumps are only recommended for temps above freezing.

 

[Ivan Seeking]

Thanks Artman! This sounds like as much a marketing problem as anything.

This almost sounds like a good undergrad project...at least: Determine if, when, and where this is feasible; the return on investment; the time for payback, etc.

If worth doing, this should automatically be incorporated into new homes and offered as an option with any new A/C or heat pump system, when appropriate.

The water heater pre-heater is also an easy one to snag. Nice! The two largest energy demands are typically space and water heat.

 

[Artman]

The water heater pre-heater is also an easy one to snag. Nice! The two largest energy demands are typically space and water heat.

The domestic water heating option is great in warm climates. During the cooling season a desuperheater added to a heat pump refrigerant cycle can meet or very nearly meet a home's domestic water heating requirements, while helping the efficiency of the cooling. It is really a win-win arrangement that pays for itself very quickly.

 

[Ivan Seeking]

The only draw back when used with a swimming pool: Now we are mixing potable water with non-potable water in the heat exchanger.

Or, do they actually have another path for the potable water? Also, is water considered to be potable after passing through a heat exchanger and/or a water heater? In fact, now that I think about it... is properly treated swimming pool water considered potable?

 

[Danger]

I don't know how things work in the States, but up here water is certainly considered potable after going through anything that meets sanitary requirements. After all, you can drink out of the hot tap in your bathroom, and all coffee makers are essentially heat exchangers (one-stage ones). Same for kettles.

 

[Artman]

In a swimming pool the pool water is circulated through the desuperheater and heated some when the A/C is operating. Refrigerant is on one side of the tube and pool water is on the other. A desuperheater used for pool water has to be made of corrosion resistant materials, such as cupronickel for the refrigerant and PVC for the water jacket, or the chlorine or Bromine or whatever chemical is being used will eat it too quickly.

I think that water heaters are considered potable, however, the temperature that the water is stored at is critical. If it is held warm, less than 110 deg F, Legionella and other microbrial contaminates can form.

 

[Ivan Seeking]

Are exchangers available that would allow potable water and pool water to circulate separately. Also, do you know if these are offered by any of the major A/C manufacturers as an option with new systems.

Sidebar: Your comment about legionella gets me to thinking about our Bunn coffee maker. I wonder if it is a good idea to turn the unit off after the next batch of water is heated. How long does it take for microbial problems to arise?

 

[Ivan Seeking]

I don't know how things work in the States, but up here water is certainly considered potable after going through anything that meets sanitary requirements. After all, you can drink out of the hot tap in your bathroom, and all coffee makers are essentially heat exchangers (one-stage ones). Same for kettles.

I have heard that one shouldn't drink from the water heater.