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Passive Hot Gas Reheat system

Passive Hot Gas Reheat system

Passive Hot Gas Reheat system

We are installing additional cleanrooms in our aseptic pharmaceutical filling operation. The AHU that the engineering firm specified has what they are recommending a "passive hot gas reheat" system that utilizes a closed refrigerant loop with flow control to cool/dehumidify the mixed air and then reheat the supply air. It will provide tight humidity control with improved energy efficiency. I am not familliar with this type of system.

This "Thermosyphon" system pretty much shows the general arrangement...

Does anyone have experience/opinions with this they would like to share?

RE: Passive Hot Gas Reheat system

Concept of heat pipe presents common knowledge for long, while the system you refer to is apparently proprietary system.

Explanation looks logical, they likely tested it before releasing to market, and now it is only real operating data that can confirm the concept over time.

Cost-benefits analysis makes sense during specifying stage of project, I don't know what would you need to do now. Do you have any specific question?

RE: Passive Hot Gas Reheat system

That is not the system that is proposed, just an example. What is the common nomenclature for this type of system?

I was hoping for some operators to weigh in and have opinions (i.e. headache/great/doesn't do much).

RE: Passive Hot Gas Reheat system

I have not head it described as a "passive hot gas reheat" system before, but it is essentially a "heat pipe" system. The passive I suppose refers to the fact that there is no compressor. They work, but I don't know about the ROI.

Looks like your actual cooling coils are chilled water. There are DX units that use the actual hot gas from the compressor to reheat the air, but that does not appear to be the case here.

RE: Passive Hot Gas Reheat system

YES! That's the term I was looking for. I feel a little silly having not known what that technology is called, since it's not a new concept.

As for our units, yes, they are chilled water cooled.

Since we require tight humidity control (application is a pharmaceutical cleanroom) there is a lot of extra energy expended to cool/dehumidify and then re-humidify the air. I can't imagine that adding a system like this to an air handler wouldn't provide a relatively quick ROI. Once we get the detailed designs complete, there should be performance data from the manufacturer that can be used to estimate the energy savings.

Thanks for the help!

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