Hot Gas Bypass

Brad White_200

http://www.achrnews.com/Articles/Technical/BNP_GUID_9-5-2006_A_10000000000000131938

I just gave it to one of my apprentices to save me some time, coincidentally.

BTW: Lately I am making use of Rawal APR valves which allow modulation and negates the need for hot gas bypass. Not what you are asking, but I am really coming to appreciate these devices.

Economizer

Hot Gas Bypass Control

I understand hot gas bypass controls the capacity of a system, allowing the compressor to maintain operation while the load decreases, which decreases compressor on/off cycles. What I don't understand is how is this controlled.

Say for example on a 10-ton system the evap is only picking up 8-tons, so the TXV will let in less refrigerant... (this is where my brain stops working). Can someone please explain what is modulating the hot gas bypass valve, on an external HGB line.

thx

Hvacman

I think of it like this...

In a comfort cooling application the HGBP valve adds hot gas to the suction line whenever the suction line pressure drops below a set point. This does 2 things, it prevents the evaporator coil temparature from dropping below freezing and because the gas is already saturated it won't try to absorb BTU (that already are in short supply). The HGBP valve modulates off the suction line pressure, we already know if we keep the coil pressure up the temparature of the coil will stay up because of the P/T relationship. Hope this helps.

I'd add too that not all HGBP valves are mechanical, just as we now have EXVs. Say it together now: stepper motor!