Smart questions
Smart answers
Smart people
Join Eng-Tips Forums

Member Login

Remember Me
Forgot Password?
Join Us!

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips now!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

Join Eng-Tips
*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.
Jobs from Indeed

Link To This Forum!

Partner Button
Add Stickiness To Your Site By Linking To This Professionally Managed Technical Forum.
Just copy and paste the
code below into your site.

Fred3 (Civil/Environmental) (OP)
17 Aug 07 14:29

I am a chronic do it yourselfer and I am putting some serious thought into converting my old electric tank water heater into a water preheat tank for my tankless gas water heater.  It will be preheated during the summer by a through-the-wall unit mounted in the garage blowing cold air inside the house and expelling heat into the water tank and (vented) garage.  The A/C will be fitted with a shell and tube consenser in series with the current condenser.  I have not been able to find a small window unit employing R134a, which is the only ype of refrigerant I can use since I am not licensed for anything else.  When the R22 is removed for the modification, what can I do to get the same performance from R134a?  I am afraid that if I make these modifications I will not be able to find anyone that will charge it back up for me.
MikeHalloran (Mechanical)
17 Aug 07 20:43
Even if you were licensed to do it, I don't think it's a good idea, because any refrigerant leak would go into your potable water.

How about making up a water to air exchanger (like a refrigerant condenser, but don't use a used one), and strap it onto the hot air exit of the a/c condenser?  Yeah, it's probably inefficient, but you're recovering waste heat, so who cares?

Mike Halloran
Pembroke Pines, FL, USA

tbedford (Mechanical)
17 Aug 07 22:59

another problem...
the R22 compressor has a different pumping capacity than R134...
don't expect much heat

chilled (Mechanical)
18 Aug 07 1:00
To get the same performance from R-134A as R-22, don't you just add (134/22 x 1) as much refrigerant to the new system??
MikeHalloran (Mechanical)
18 Aug 07 1:18
No, that isn't how the refrigerant numbers work.

Mike Halloran
Pembroke Pines, FL, USA

willard3 (Mechanical)
18 Aug 07 11:50
Rather than try to guess the properties of refrigerants, you should get pressure/enthalpy diagrams and tables from the manufacturer or ASHRAE volumes.

When you compare the properties of 134a and R22, the problems will become obvious.
imok2 (Mechanical)
18 Aug 07 14:29
I believe this is your best bet fo a retrofit
ISCEONĀ® MO59 is an easy-to-use, non-ozone-depleting HFC retrofit refrigerant for R-22 in direct expansion stationary air conditioning (AC) and medium-temperature commercial refrigeration systems.
rmw (Mechanical)
18 Aug 07 21:09
A unit was made about 20 years ago to do just what you want to do.  Maybe you can find one.  I have two in the garage that I am trying to give away.  Mine were branded by Lennox, but they didn't manufacture it.  I forget who did, but all the major brands put their name on them.

It installed between the compressor discharge and the condenser and had a pump that circulated water from the water heater tank no matter what the heat source would be.  It lowered the head pressure and helped the unit's efficiency.

A neighbor installed one on a 3 ton home unit (R-22) when I bought mine and it worked too good.  It made more hot water in an hour than he could use in a day with a family of four.

Plus, it produced water at about 190F and after a while (about an hour) the tank saturated at 190F.  It lost its effectiveness (on the A/C side) at that time.

He and I both had small children, 2-3 years of age, and upon seeing how well his system worked, my wife forbade me from installing mine.  I agreed with her that the potential for scalding a kid wasn't worth the savings on the light bill.  So I still have them.

Fred3 (Civil/Environmental) (OP)
20 Aug 07 14:40

That is an interesting device you have.  What part of the country do you live in?  It would be handy if you were in North Texas.  I had planned on using an ac unit with manual controls and then use the water heater's thermostat to kill the power when it reached 120F.  If I had one of these, I could just kill the power to the pump with the thermostat.  The initial idea was to use the central ac, but proximity to the water heater was an issue, but since this is so effective, it would be worth the extra 30 feet to save a lot of work building stuff.
absrbrtek (Mechanical)
25 Aug 07 22:47
Id be interested in getting those htexs from you if your gonna just unload them. Id like to tie them into a pool to help heat it up.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!

Back To Forum

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close