Glycol concentration for make up air units 3

[oooaaa]

I currently have a project which recoverys heat from condensers to preheat make-up air. My question is how much glycol concentration is proper for make-up air roof top unit? my concenption is that even at night the unit is shutdown, the water loop still keep on runing, therefor, it is not necessary to put the water solution freezing point lower than winter design temperature which would result in high concentration on the water loop system. Thanks for opinions and recommendations

 

[DrRTU]

If your OA temp will go below freezing then you are going to require a low temp. heat transfer fluid. You could have a pump failure, loss of power or the system could be drained for maintenance and still have a water slug in the coil. I like to use Dowtherm.
If you your max temp is less than 250 F use SR-1. Pick your min. OA temp.

http://www.dow.com/PublishedLiterat...rans/pdfs/noreg/180-01312.pdf&fromPage=GetDoc

 

[GMcD]

Use Dowfrost- propylene glycol- a lot more environmentally friendly than the the ethylene glycol. And make sure it's the proper inhibited type with additives for closed loop hydronic systems. Normally 25% to 30% is enough for adequate freeze protection, even on the Canadian Prairies. At those concentrations the fluid will go to mush but won't freeze solid, and it will buy you enough time to deal with the problem.

 

[ChrisConley]

Actually here on the Canadian Praires we frequently go all the way to 35% for burst protection at -40F. Also, if you're using inhibited glycol at 35% your chemical treatment is mainly handled by the glycol.

 

[oooaaa]

The winter design temperature is -12deg. F in my case, since there is a dry cooler in the system which need not function in winter, some people saying that we should us 50% propylene glycol, without the experience of glycol concertation in hudraulic system, besides the increasing of pressure loss of the system and decreasing compressor efficiency, I could not figure out other disadvantages , but I am so hesitate with this figure.