I haven't used a Rawal before. I always calculate my own loads and perform my own selection of part numbers based on the application. So can't comment on the brand, but to me they are a widget/part number designed to sell HGBP to the masses without anybody having to understand the mechanics of HGBP.

In your case, a 1-1/2 ton HGBP system on a 3 ton system is acceptable if (when you need ANY cooling) you always have a 1-1/2 ton load or greater. The HGBP will then handle the other 1-1/2 tons (or less) and the unit won't cycle.

99% of the time, I size a HGBP unit for 100% (or nearly 100%) bypass capacity so that the unit won't ever cycle except on a complete lack of load. However, there are applications where they have a 50% load (or greater) or no load....no in between on the low-load side. This could be your situation as well.

 

What is the present problem that this new modification will solve? Why do you need the HGBP?

PHM
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Underground storage facility. Steady temp of 62 degrees ambient. Temp and humidity controlled. No load on evap.

 

Hey if boss says then it,must be right lol. But the valves do work well.

 

Call Rawal. They help help you size the valve for your application. Those guys are very helpful and pick up the phone right away. I have installed about 12 or so. They do a good job. Please install ball valves on the lines going to the Rawal valve like the instructions state for troubleshooting later on.

 

I have a system that needs HGBP. I have to introduce it into the suction line at the compressor. [/QUOTE

Typically to size the HGBP valve is around 30% of total capacity. Also why do you need to introduce the valve to the suction line, AT the compressor?? Seems like chasing SH would be quite difficult in your application.

 

...Typically to size the HGBP valve is around 30% of total capacity...

That is not accurate. Sizing to that low of a capacity percentage would not accomplish much in most cases.

I should add that the sizing requirements should be of the smallest stage or the largest compressor capacity if the system could balance the compressor starts/hours in a multi-stage system.

 

I'm sorry - I started talking about HGBP because I forgot that you already had the Rawal valve. If you already have the Rawal valve just use it. So far as I can understand them all they are is an expansion chamber in the suction line into which HG is injected. Incorporated in with that is a desuperheating liquid injection valve into the same expansion chamber - to control compressor inlet temp under very low evap load.

BTW: How much do Rawal valves cost? It is the same or less than doing it yourself with off-the-shelf parts?

 

They could have done a better job putting this device together.

 

Does anyone know what is inside that expansion chamber part of the Rawal device? Is it baffled in any way? Or maybe contains a mesh or something? Or is it just pretty much a hollow tube with two refrigerant valves attached?

PHM
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Update.

I installed the APR valve today. System is running fine now. While on the job site I looked over 2 more split systems that need piped and started. They are Trane condensers with factoy installed Rawal valves. Couldn't believe it.

 

You can special order them. Or you can pipe them yourself before its put in.

We will take new units are our shop and add extra valves to them before sending them out to the job.


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We have used several of the Rawal valves . They will help with over sized systems especially in dual circuit systems just make sure it is always the lead circuit .

 

I ran across some recently that were used to set 48F constant evap air discharge temp, it didn't work out very well. They were field installed on 20 ton York condensing units.

 

Suction pressure based HGBP valves (or any suction based capacity control) don't work very well...long term. They don't account for coils getting dirty.