Water pipe insulation questions.

[inhotwater]

I would like to get your opinions on insulating pipe for water heating systems, with underground burial. 1triplewrap.jpg I see lots of sellers of Pex pipe, such as this:

It seems to me that having the hot water pipe and the return line in such close proximity and with minimal insulation between them, would not work very well. I am looking at this for both domestic water and swimming pool heating.
The pool heater people tell me they usually just put the bare pipe directly in the ground with no separation or insulation.
They say " it works fine, don't worry about it"

What do the experts recommend?

[Mike90250]

With circulating heat systems, there is little (should be) difference between inlet temp and outlet temp. If there was, part of your slab would be cold, and part hot, instead of evenly warm. So I'd not worry about pipe-pipe. The bundle needs to be insulated from the heater to the slab though.

[LucMan]

It depends on how far your running your piping, ground temperature, and what temperature water you are running under ground. How much losses are acceptable to you or the system that your installing?
I recommend Uponor ecoflex if you need insulated under ground piping. Or you can make your own with 4" solid schedule 20 PVC drainage pipe as an outer jacket covering, and slip Armaflex type rubber insulation over the piping in the jacket.

[J.P.M.]

Your surmise on line proximity is correct. The closer proximity and/or less thermal resistance between supply and return lines, the less efficient will the system be. For short runs and so smaller heat transfer area between hot/cold lines, the less will be the penalty, but the penalty will always be there. Supply and return liners is contact/close proximity will act using the same principles as a countercurrent heat exchanger in preciely the wrong (worst possible) location. Now, if it costs a boatload of money to separate the lines compared to the incurred costs of a very good thermal design exactly where it's least wanted, then separating the lines may not be worth the cost, but that's a slightly different consideration than what's a thermally efficient design.

For hydronic space heating or for domestic water heating or any design where the point(s) of use are separate from the point(s) of generation, assuming the design is safe, all lines except those that are used to dispense heat should be insulated for max. cost effectiveness.

For underground use, make sure the insulation is fit for the intended service and appropriately wrapped.

[bcroe]

They say " it works fine, don't worry about it"

Most of the time that actually means, they either do not know how much difference it
makes, or they do not care or think you will find out. Check your source carefully.
Bruce Roe

[peakbagger]

The outdoor boiler folks use a duplex line with PEX lines surrounded by a high density foam that has no void space. One thing to consider is burying pipe underground in wet soil can really suck the heat out of the piping. If there is ever standwater in the trench it really can hurt things. Unfortunately in poorly draining soils the actual installation of the trench causes it become a drain with water running down the line.