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Thread: discharge bypass valve noisy.
08-05-2012, 08:14 PM #1Professional Member
- Join Date
- Jul 2009
- Northeast, Md.
discharge bypass valve noisy.
It is a 7ton split system constant volume air handler supplying to 8 VAV's. They have a VFD to control fan speed by static pressure. Obviously when VAV's are closed, and outside air is closed VFD ramps down to below 30hz. (50%). They are using a discharge bypass valve to control suction pressure due to this loss of airflow. When the hot gas bypass opens it does not regulate, but just rushes hot gas in at a noisy rate. almost like air brakes coming on in a tractor trailer. Then it hunts and keeps doing it over and over again.
The system is equipped with the HGBE-8 pilot operated valve. I contacted sporlan, and they say the valve is too big. They say the HGBE 5 is what i need for a 7 ton application. I ordered it and will see if that works. I was just wondering if anyone has experienced this, and if someone could help me with sizing a HGBP valve that would be great! They are sized in capacity released and not tonnage of unit.
08-05-2012, 08:22 PM #2Professional Member*
- Join Date
- Jan 2008
- Dallas ,Texas
I assume you are having issues with this unit?
08-14-2012, 08:14 AM #3Professional Member
- Join Date
- Apr 2002
- most of the time in the Philippines
08-14-2012, 09:02 AM #4
Here's how you size a DBV (and it requires a lot of guesstimation):
1- determine your lowest load condition. Let's say you've got a 10 ton application and you determine that your low (or minimum) load condition would be 4 tons.
2- determine what your minimum suction pressure is going to be. For A/C applications it's typically the pressure equivalent to 26F.
3- from the mfg equipment specifications determine the equipment capacity at your minimum suction pressure and expected discharge pressure. Let's assume that to be 9 tons.
So, you have a piece of equipment operating at your minimum suction pressure condition rated at 9 tons, and the anticipated load at the minimum condition is 4 tons. You've got 5 tons of extra capacity....so you need a DBV capable of bypassing 5 tons of discharge vapor.
Typically, a DBV with a rating equivalent to 50% of the equipment rating will be sufficient.