Regarding your previous post, sorry for chopping your post up into small bits, but I find it the best way to comment, and/or answer your many questions:
“But it seems pretty cut and dry how it works or correct if i am wrong similiar in nature to a TXV”
In terms of being a dynamic valve (one that reacts to the refrigeration systems changing conditions) you are correct, in terms of being an operational valve that is always in the refrigeration system, it is not. Even when this valve is installed in a refrigeration system, it is only used when it’s needed. Under most operating times this valve will not open, and therefore will not affect the operating characteristics of the refrigeration system at all.
“it senses the suction pressure from the suction line leaving the evap”
Although it can do that, depending upon the actual valve model used, it senses either the outlet pressure of the valve itself, or the pressure at the end of the equalization line that it may have. This equalization line, if used, senses suction pressure after the evaporative coil assembly as you’ve pointed out.
“if it is below a minimum setpoint the valve opens allowing hot gas from the discharge line to enter between the TXV and distributor on the evap”
Here again, depending upon the refrigeration system itself, the introduction of the discharge hot gas can either be at the junction you’re referenced, after the evaporative coil assembly altogether, upstream of the suction line accumulator, or after the suction line accumulator.
“and then as the coil temp rises back above the setpoint it closes again.”
Remember, not by temperature, but by pressure. As the pressure of the evaporative coil and/or suction line drops below the preset value, then the valve starts to open, as the valve starts to open, it throttles itself to maintain the evaporative coil/suction line pressure precisely, then as the pressure rises to the point of the preset value again, it closes altogether.
In conclusion, it’s only used when it’s needed, and it’s setting is preset, so automatic operation is possible.
And now to my question from you:
”What I would see as a big advantag in using this kind of HGB valve would be in conjunction with a EPR valve. The EPR to mainain an constant evap temp of lets say 30 degrees and the evap HBG to prevent the coil from icing which is kind of the idea I was getting at in my post to the original question. So the coil would always be as cold as possible and this kind of HBG would prevent it from icing. I would think using the two together would then easily maintain serverrooms 65 degree desired temp easily.”
You have to remember that the main function of this valve and process, is not to maintain the coldest evaporative coil temperature possible, but rather to “prevent” the evaporative coil surface from freezing. In that function, this would be the only valve required to complete the task.
In fact, if this valve process were installed, then Serverroomcooling could set his thermostat down as far as he’d like, and never have to worry about icing up the evaporative coil surface again.
Not that we would recommend this practice to him, but he could technically set the thermostat to 40 degrees F, and the system would continue to operate without cycling the compressor off, and the server room temperature would settle at the point of system capacity equalization, somewhere between 70 and 40 degrees, and would vary in temperature only as the outside ambient and building’s central HVAC system affected the server room’s HVAC system. But of course, we would never recommend this to him for the obvious reasons (ie. humidity condensation, energy conservation, compressor life expectancy reduction, room overcooling, and the like).
This elimination of evaporative coil surface freezing is exactly why this valve and process was originally designed, and therefore is exactly why I first recommended it after finding out that Serverroomcooling wanted to operate his system below the traditional operating standard of 72 degrees F.
Any more questions or comments my friend?
John J. Dalton