ReplyPut in a Rawal valve. http://www.rawal.com/ Much better control than a strait HGBP.
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I need to add a hot gas bypass to a 4 ton unit. the unit cools a MCC.
Any in-put on valve size
I will be adding a VFD-66 speed controler for outdoor fan also.
Professional Member
Put in a Rawal valve. http://www.rawal.com/ Much better control than a strait HGBP.
To much work with too little time!!!!
Professional Member
Where are you injecting the HGBP?
If it's at the TEV outlet, all of the distributor tubes, if you have a distributor, need to be increased one pipe size for proper operation. Most don't do it, but if you do, it'll really control evap temp smoothly.
Sporlan has/had great info on this.
I'd also add a compressor discharge temp limit stat for low charge protection. I usually use a strap-on Aquastat.
Jogas
Four wheel therapy, my 1968 Camaro is gone and will be missed
Professional Member
Why both a hot gas bypass and a head pressure control, why not just the head pressure control? Is your suction pressure that low ???
How much copper are you adding to get the hot gas to the evaporator?
Is this for Humidity control?
Split system or Package?
UA Local 141
Professional Member
Head pressure control is required when using HGBP as part of the discharge gas is going to the evap, not the condenser, which is now in effect oversized. We've added VFD's to condenser fan effectively for this situation.Originally Posted by berg2666
Head pressure control will only keep the evap temp up IF the evap is seeing it's normal load. HGBP is designed for partial EVAP load operation because the evap is NOT seeing it's normal load.
Jogas
Four wheel therapy, my 1968 Camaro is gone and will be missed
Professional Member
Would a motor control center be a constant / normal load?
UA Local 141
Professional Member
If it was, I would think he wouldn't need HGBP in the first place.
I'm thinking it's a variable MCC or envelope load.
Jogas
Four wheel therapy, my 1968 Camaro is gone and will be missed
Professional Member
excellent product. I have had nothing but good luck with these.
Professional Member*
Well right now the MCC has a 2 ton minisplit cooling it... they have added more equipment to the room and the 2 ton is no longer keeping up, infact it was 65deg out today and it was 78 in the room. Now when the new equipment shuts down the room comes down to 65deg. This equipment is kicked off and on now as the new system is not ready to go online but when it does not problem will be with us 100% of the time. I would hate to see what the temp goes up to on a hot summer day.
The MCC is for a SubSea Oil well system on a shell platform.
The system must be class 1 div 2 as it is located next to the well bay.
What I am going to do is use a 4ton air handler and mount it on a stand and put a 4ton compressor under the air handler, I will use a data aire condenser coil outside with a 3phase TEFC motor.
The HGBP and speed controler is needed so that the system can run in low temps... the room still needs cooling in the cold months just not as much as it does in the hot months. Also humidity control to lower the chances of arcing when switchgear is opening or closing.
They do not want a multi speed compressor ( for what ever reason ) and I dont have the room to put two compressors under the airhandler and it be serivceable. This is why I chose HGBP and speed controler route.
The other option was to have a Class 1 Div 2 unit custom made for the roof, then we must have the engineering group look over the building the ensure the blast ratting of the building will not change once we cut holes in the roof. And will take much more time to be approved for construction to start.
Professional Member
Size the valve for 50% of the 4 tons. Going larger might cause problems w compressor cooling. As you said a 2 ton was doing ok until they added more load, this should give you good results. Personally I'ld use a mini split w a variable speed compressor. Much more efficient.
Professional Member*
Finally, Ive waited 10+ years to hearaboot someone using the rawl!!!
Abs if you could start a post or post your experience with it I'd apprecite it.
If you cant fix it right, try again.
Professional Member
If the HGBP was injected at the distributor, wouldn't compressor cooling (compressor suction temp/superheat) be a non-factor?
And if it's injected in the suction line, liquid injection would solve that problem...but cost more money.
We put in a Pharmaceutical Clean Room system with a Staefa HGBP valve that was sized for the full first stage compressor tonnage. It was active all the time to trim and we controlled DAT within 2*with HGBP injected at the distributor. Worked very well.
Jogas
Four wheel therapy, my 1968 Camaro is gone and will be missed
Professional Member
CRAC with remote condensor, so how about a liebert minmate or a Stultz unit for the application.
UA Local 141
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