Heat scavenging systems ... for an A/C

[Dumber than lumber]

Who can give me some info on this?
Background - when we bought this house we live in (bought 25 years ago) it had a scavenger system. It somehow took the heat output from the AC unit and used it to circulate water through the electric water heater. The calim seemed to be that it also made the AC system more efficient.
When we had to replace the AC system (over 20 years ago) we were advised (by the AC contractor) that these scavenger systems had a not-insignificant risk of causing serious damage to the internals of the AC system. (I think our household electric bills went up about $8 per month when we had the scavenging system disconnected.)
What is the current status of this technology, and the return on investment of these systems?

 

[Kaizen]

Wow did it have Freon pipe running through the tank going back to condenser?
Latest I’ve seen is for all electric is a tank with a heat pump on top. Takes heat from the room it’s in. Has an electric backup. Pricey


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[nadogail]

IMHO, The idea was to preheat the cold water going into the water heater. The amount the cold water temperature was raised reduced the requirement for adding additional heat to the water in the hot water tank.

IMHO, it is basic thermodynamics.

 

[theoldwizard1]

What is the current status of this technology, and the return on investment of these systems?

I can not say I have seen any systems like this for domestic hot water, but I have seen similar systems that are used to heat swimming pools. The problem i, when you really want your swimming pool heated the temp are probably too chilly for A/C. You probably don't need the swimming pool heated when the ambient temps are in the 90s !

IMHO, The idea was to preheat the cold water going into the water heater. The amount the cold water temperature was raised reduced the requirement for adding additional heat to the water in the hot water tank.

IMHO, it is basic thermodynamics.

Yes, but a heat exchanger only works when both fluids are MOVING ! The swimming pool concept works because the heat exchanger dumps the hot water to an "infinite" heat sink via a pump. In a home, the heat exchanger needs to be inside of a storage tank.

 

[slow]

https://techcrunch.com/2011/06/12/air-conditioning-water-heater/

My parents have had a setup like this, (different brand, but same concept) works great, My dad turns the breaker off for the water heater for around 1/2 the year. I helped replaced the water heater when the tank started to leak last year, The water coming into the water heater from the recovery unit was HOT with just a single pass through the system. It was hard to find an HVAC contactor who would install it, as most said it would void the warranty. Both units have run for 15 years without issue, and the original AC was replaced at 15 years old as preventive maintenance they replaced the recovery unit with a new one of the same model

edit, The one they have is not just a preheat, it connects to both the bottom and top of the water heater and has a circulation pump to keep the water in the tank hot.

 

[jlv03]

Home Depot has a ZeroEnergy Heat Recovery device. No experience, the idea intrigues me but natural gas is so cheap these days it makes it hard to justify the expense.

https://www.homedepot.com/p/ZeroEne...-Heater-System-Zero-Energy-ZE-TSHRU/203715807

 

[slow]

no natural gas around here and the AC runs 9+ months a years, makes economical sense, especially when the water heater and ac are on opposite sides of the wall. My house, there is a large amount of living space between the 2 so I would not install one here.

 

[Dumber than lumber]

https://techcrunch.com/2011/06/12/air-conditioning-water-heater/

My parents have had a setup like this, (different brand, but same concept) works great, My dad turns the breaker off for the water heater for around 1/2 the year. I helped replaced the water heater when the tank started to leak last year, The water coming into the water heater from the recovery unit was HOT with just a single pass through the system. It was hard to find an HVAC contactor who would install it, as most said it would void the warranty. Both units have run for 15 years without issue, and the original AC was replaced at 15 years old as preventive maintenance they replaced the recovery unit with a new one of the same model

edit, The one they have is not just a preheat, it connects to both the bottom and top of the water heater and has a circulation pump to keep the water in the tank hot.

Terrific rundown on what sounds like a similar or better setup. Thanks

 

[firebirdparts]

It would make sense to take that directly off the compressor, where it's hottest. That is interesting, and I've never seen one installed.

I have seen that heat pump water heaters are now perfectly normal for electric water heaters. They would be inadvertently air conditioning the space with a separate compressor.

 

[SGKent]

I suspect the discovery of Legionnaires disease somewhat raised the liability on a system like that.

 

[TRWham]

Heat recovery from HVAC and especially refrigeration is common, even ubiquitous, in large commercial installations like supermarkets. With maybe a million Btus available from a typical supermarket system to heat water, it would be silly to blow all that heat off into the atmosphere. You already paid for it- might as well use it.

Some or all of the discharge gas from refrigeration is diverted to the reclaim tank where they use the same basic plate heat exchangers that are used for milk chillers, but in reverse. The cooler gas is then sent to the condenser to finish condensing. The downside of preheating water fed to a water heater is lost heating capacity in the water heater. Between heating water, and heat reclaim for space heat, much of the heat from refrigeration can be recycled into the space during the winter.

I did know one guy who installed one at home, but he had been a sales rep for Paul Mueller, which is one of the major suppliers of these (the other being Therma-Stor).

 

[TRWham]

I suspect the discovery of Legionnaires disease somewhat raised the liability on a system like that.

Not really. Legionnaires' is an issue for open water loops, and systems with water accumulating in ductwork or drain pans. The water side of these heat recovery systems is only open at the point of use and there is no recycling of water. The refrigerant side is obviously closed.