hi-temp water reduction
hi-temp water reduction
(OP)
Hey all,
Problem: I'm using hot water in a standard air handler heating application where I've called for 200 deg F water in and perhaps a 20 deg drop through the coil for my heating needs. It turns out the existing hot water system I'm tying into varies in temperature from 200 to 300 deg's F. (say 215 at 170 psi and 316 @ 220 psi). If my coil or other associated components can't handle the elevated temperature (control valve, piping specialties, etc.), what are some simple options for reducing the temperature in the mech room before I get to the coil? I'm open to any ideas such as pressure reducing valves, heat exchangers, blending, etc.
Thanks in advance.
Problem: I'm using hot water in a standard air handler heating application where I've called for 200 deg F water in and perhaps a 20 deg drop through the coil for my heating needs. It turns out the existing hot water system I'm tying into varies in temperature from 200 to 300 deg's F. (say 215 at 170 psi and 316 @ 220 psi). If my coil or other associated components can't handle the elevated temperature (control valve, piping specialties, etc.), what are some simple options for reducing the temperature in the mech room before I get to the coil? I'm open to any ideas such as pressure reducing valves, heat exchangers, blending, etc.
Thanks in advance.





RE: hi-temp water reduction
TTFN
RE: hi-temp water reduction
RE: hi-temp water reduction
Either arrangement saves heating energy as well as providing good temperature control.
RE: hi-temp water reduction
RE: hi-temp water reduction
You are obviously taking a proactive posture in this situation. That’s good. But having the information regarding the variance in temperature and pressure, wouldn’t it be also proactive to verify that you might only have to change a few components to withstand the changes pressure and temperature and take advantage of the greater delta T.
The pressures and temperatures do not seem to be that extreme IMO. Step back and take another look at it. Keeping it simple may pay off in the long run.
New Years Greetings
pennpoint
RE: hi-temp water reduction
h
To optimize energy usage, you should mix hotwater with coldwater, reduce temperature and use in the AHUs. You may not be able to recover useful energy if you use any other heat transfer devices.
Regards,
RE: hi-temp water reduction
If I have got my conversion right, cooling coills/heating coils are normally designed for working pressures of around 150 psi.
HVAC68
RE: hi-temp water reduction
Design your system for 200-20=180°F return water tempeature from both the primary & secondary system. Thus the secondary system will be 200°F supply and 180°F return. The primary system supply will vary from 300°F to 215°F supply but design primary return for 180°F. Temperature rise at secondary therefore is 20°F but is 120°F to 35°F on the primary.
For say 500,000 Btu/hr load:
Secondary gpm = 500000/(500x20) = 50 gpm
Primary gpm with primary at 300°F = 500000/(500x120) = 8.333 gpm
Primary gpm with primary at 215¯F = 500000/(500x35) = 28.57
Check mix T at 300°F primary:
Mix T °F = (8.333x300+(50-8.333)x180)/50 = 200 Check!
Check mix T at 215°F primary:
Mix T°F = (28.57x215+(50-28.57)x180)/50 = 200 Check!
RE: hi-temp water reduction
lilliput: regarding your response, I will check out those B&G manuals when I return to the office on Monday. It's weird how we all maintain similar resources. Thanks for the detailed analysis. I assume your primary/secondary solution was similar in concept to what KDMKE was describing in the first part of his/her response.
Hopefully when Trane finally get's back to me on their coil capabilites/limitations, it will be a lot simpler matter. These ideas will help me have some "worse case" alternatives. Thanks again all.
RE: hi-temp water reduction
I checked out that B&G section today. Now I see what you were getting at--you were right on. This does seem like the way to go if I find out that the coil can't handle these higher conditions. If I get to that point I may have to start a new thread to make sure I'm sizing the secondary pump correctly!? Thanks again for the help!