Heat Recovery Unit hooked up with AC

Problems related to residential installations.

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Heat Recovery Unit hooked up with AC

Post by wulianlian » Tue Aug 02, 2011 11:55 am

I am a college student doing a report on AC hot water heat recovery
systems. Several AC professionals and alternative energy specialist
tell me that in the 80's they recommended and installed many of these
heat recovery units, but they no longer recommend them or install
very many. They said that modern AC units make heat recovery less
beneficial and can, in some cases, create problems with the AC
systems. After looking into the question, I am having difficulty
understanding what are the problems with the heat recovery systems as
an add-on to modern AC units. Can some of you AC professionals out
there please point out some of the specific problems as you understand them?

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- Heat Recovery Unit hooked up with AC

Post by heatseeker » Wed Aug 03, 2011 1:53 pm

outdated technology---- Time to upgrade while you still can

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- Heat Recovery Unit hooked up with AC

Post by Freon » Sat Aug 06, 2011 2:15 pm

Heat recovery may become economically viable but today it's no there yet, in my opinion. Everything you're researching involves thermodynamics, specifically, heat transfer. Heat transfer is not a lossless process and that's the first big problem. The second is once recovered, how to you propose to store the energy? Thermal "batteries" may be viable but now you have a large added cost in the 'battery". Direct use in another thermodynamic process is possible but again suffers from the fact heat transfer is not 100% efficient. So when it's all said and done, you reclaim so little energy for the cost that it's not feasible.

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- Heat Recovery Unit hooked up with AC

Post by nomadpeo » Thu Aug 11, 2011 8:06 am

the heat rejection at the condenser is a combination of latent heat absorbed in the evaporator plus heat of compression. the bulk of heat generated from the phenomenon that happens when the gas is compressed (nature of the beast) has to be released first before the refrigerant can begin to condense in the condenser. carrier and others used to sell a heat exchanger that could be retrofitted in series with the discharge line leaving the compressor. the heat of compression was transferred to a water loop which circulated through the water heater. this heat, which was previously wasted, was used to pre-heat the water heater, thereby saving energy cost of heating water.

initial cost of installation, relatively slow payback and potential for component corrosion over time all contributed to the industry abandoning the idea for the most part. they were problematic and that outweighed the profitability. in these days of 'green' awareness, the idea is still a good one and still used on a larger, commercial scale.

higher efficiency air conditioners provide energy savings that matches the savings of the heat recovery system you are referring to without all the complications. also, heat pumps recover this compressor discharge heat to heat the house in the winter.

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