change from GRE pipe to HDPE pipe as chilled water piping

[hollandhvac]

Gents,
I have been asked to change from GRE piping to DHPE piping for our underground chilled water supply system.
The Existing GRE has worked very well and I do not want to change. But others think different about this new part of underground chilled water piping.
What is your experience. Change to HDPE or keep GRE.

 

[EnergyProfessional]

I assume the "others" determined the GRE is deteriorated and needs to be replaced? I assume if it was in good condition, there would not be talk about replacing?

 

[hollandhvac]

No, we have an existing system that is made of GRE pipe. We are now getting a new system where our contractor states that taking HDPE is a better choice than GRE.

 

[MintJulep]

Better choice for the contractor's profit.

 

[Compositepro]

Unreinforced plastic pipe will have a significantly greater CTE(coefficient of thermal expansion). This may or may not be a problem where temperature cycles.

 

[Ziggypump]

I worked in an office where they used HDPE for the entire geothermal system. Seems to work fine. My only issue with HDPE is the sizing method.

HDPE pipe utilizes the iron pipe method. While this may not be too much of an issue with smaller pipe, it can come back to haunt you later. See this Link for information regarding pipe size and wall thicknesses. I believe DR9 is common for geo systems, but each size has it's own pressure rating so be careful with use in a chiller system.

Don't for one minute think the pipe sizes will be a 1 for 1 swap. A project I was a part of called for an 8" HDPE pipe from the geo field to the building. The pipe was installed and when revisited to run the calcs, the head requirement on the pump was much greater. To achieve the design intent of the system and 10" HDPE pipe would need to be installed, to get the 8" internal diameter. The pump went from a vertical inline to a double suction (the 8" HDPE pipe was rather long).

I suggest revisiting the calcs before allowing this change. It may not be cost effective in the long run.

 

[rconner]

Just a question - if lines are to be insulated, and hdpe is more outwardly permeable to water than alternatives, what will be effect on insulation?

 

[Edwin22]

I would like to ask regarding the piping in FCU/HVAC, is it possible to install black steel pipe or copper pipe in the piping of FCU/HVAC and what standard I will use to justify that both can be use.