Which do you use/prefer/recommend.  I've had what sound like good arguments for a NP system from one person; but my soon-to-be installer does not care for them.  He views them as a bandaid fix for an improperly set-up system.  He said if the loop/pump system is done correclty, there's no reason to go non-pressurized.  The other side I'm hearing is that a NP system has less wear and tear on parts because of the lower pressure requirements when working, and no pressure when not cycling; which makes sense to me.  I'm fully willing to push my installer for a NP system if its truly worth fighting for; but I want to make sure that its worth it and not just something I'm making a pissing match out of because one other professional likes it.  Thanks!

I would do what the installer recommends. We like pressurized, other pros here like non pressure. You want him to own the system.

Non pressurized systems are essentially call back eliminators. There is a physical reason for that.
After you purge all the air out at startup, you pressurize the system. In A/C you now heat up the loop, causing the plastic to expand and causing the pressure to drop significantly. Due to that drop in pressure, gases, which had been dissolved in the Water (including Oxygen) do now participate out, forming "Air" bubbles in the pipes, which haveno where to go, make noise, can air-lock a loop circuit, and erode and damage pumps. In the past, contractors frequently had to come back and purge out again the loop.
The non pressurized flow centers purge out the mircro bubbles and replenish the water volume automatically, thus no need to come back for air purging.

We typically use non-pressurized on 90% of our installations. I think it looks cleaner and each job we can modify and custom build HDPE valves and flush Tee's where-ever we want. Some jobs that we use a common loop field on for multiple units on, we use pressurized systems.

ClimateMaster just came out with a 2.5 gallon tank that installs directly above their pressurized flow center on the return from the loop field. This tank acts like the B&D non-pressurized set-up. We were pushed into trying one on a job this past Tuesday. it worked out OK but I think the tank is on the small side and it takes a ton of room on the wall to mount. Also, it is extremely tough to view the 2.5 gallon tank level..it also worked out to about $300.00 more than the B&D set-up. i still recommend the B&D after trying the CM version.

It is purely a choice based on the specific job and the installers prefrance. I would echo that it is not a "which one is better" situation. Go with the flow on your installers choice.

We do all pressurised systems, except for our involvement with diy people. We coach about five diy's a year and the non pressurised flow center set up is a lot more foregiving to weekend geo pro's.

Hope this helps
Eric

Posted By docjenser on 29 Dec 2011 08:34 PM
Non pressurized systems are essentially call back eliminators. There is a physical reason for that.
After you purge all the air out at startup, you pressurize the system. In A/C you now heat up the loop, causing the plastic to expand and causing the pressure to drop significantly. Due to that drop in pressure, gases, which had been dissolved in the Water (including Oxygen) do now participate out, forming "Air" bubbles in the pipes, which haveno where to go, make noise, can air-lock a loop circuit, and erode and damage pumps. In the past, contractors frequently had to come back and purge out again the loop.
The non pressurized flow centers purge out the mircro bubbles and replenish the water volume automatically, thus no need to come back for air purging.

Would "pre stretching" the loop eliminate or improve this as a potential issue?  The installer who is recommending the pressurized system said they pressurize the loop to 150psi to take the elasticity out of the HDPE.  He stated that, by doing this, it eliminates the need to go back later and modify fluid level.  Sound reasonable?

While pre stretching sounds good in theory, there is no gaurantee that the loops will not have to be goosed up in pressure later. Our experiance has born out that some systems need to be goosed down the road, and some do not???? Fixating on choosing between the two types of circulation IMHO is wasted brain energy, they will both work well.
Eric

We almost exclusivly do pressurized with pressure bladders on our loop setups. While the pressure bladder is not a perfect solution it gets ride of a lot of the expansion and contraction of a system and we have found them to work well. The last system that we had to repurge was one that was a preexisting loop. All the new installs are (knock on wood) working great with the bladders.

Here's another alternative (not necessarily better or not as good):  My loop is pressurized at city water pressure, with no tank, and has an air vent attached to the line.  Here's a picture:



Coming out of the (in the attic) GSHP unit (Leaving Water), loop water flows through a check valve (I have 2 GSHP units connected to the loop) and heads outside to the bore hole field.

In front of the check valve is a connection to city water.  City water pressure is typically about 60 psi or higher.

City water has to pass through first a control solenoid (Honeywell), which is set to turn on once per day (via a Grasslin Digi 20 Series 24 Hour time switch installed inside the GSHP's control electronics area).  Then, city water flows through a pressure regulator before connection to the GSHP loop water.

Connected at the point where city water attaches to the loop is an air vent (Spirotop Automatic Air Vent).  It picks up air from both city and loop water lines.  It's installed, by the way, at the highest elevation point of the loop water HDPE pipe.

I believe the science here is a loop system at a constant pressure year round, in spite of HDPE pipe contraction/expansion due to earth temperature variations, and without the need for a pressure bladder tank.  It also provides a way to automatically remove air to reduce/eliminate the need for maintenance (call-back) air purging of the loop line.

My purge ports, by the way, are outside, in the lawn, just before the loop manifold.

Best regards,

Bill

Bill,
Was your set up done that way intentionally from the beginning? Or was it done due to a leak in the loop field?
I have seen that done to correct for an unknown leak outside somewhere, but never upfront in a residential application. It is definately a belt,braces,suspenders approach. The control solenoid I have never seen! A true super delux!
Eric

Posted By strawmyers on 30 Dec 2011 01:37 PM
The installer who is recommending the pressurized system said they pressurize
the loop to 150psi to take the elasticity out of the HDPE.  ...  Sound reasonable?

Sounds like a deep misunderstanding of basic physics. A pressurized loop MUST remain
elastic, because the water inside expands and contracts with temperature changes. If the
pipe wasn't elastic, it would burst.

Anyhow, "pre-stretching" does not change the basic physical properties of HDPE -- the
plastic still expands and contracts with temperature ...and with pressure.

Posted By waterpirate on 30 Dec 2011 05:03 PM 
Was your set up done that way intentionally from the beginning? Or was it done due to a leak in the loop field?
I have seen that done to correct for an unknown leak outside somewhere, but never upfront in a residential application. It is definately a belt,braces,suspenders approach. The control solenoid I have never seen! A true super delux!

Eric, like the advice being offered in this thread, I accepted the hydraulics design 'as is' from my installer.  This is what he was comfortable with.  So yes, my set up was done from the beginning as I illustrated earlier in the thread.

As far as I know, there is not a leak in the loop field.  Perhaps this was one of the objectives of the design: eliminate maintenance call-backs in case one were to develop.

I'm not a hydraulics expert, and thus don't appreciate the complete science behind my water loop design.  Actually, hydraulics isn't something I'm good at at all, and thus I don't have appreciation for why I don't have a pressure bladder tank while others do, why I have a connection to city water when no one else I know does, whether or not the automatic air vent really work, and overall if my water loop design is the most cost effective of all possible designs.

If I was an installer and was willing to think out of the box, I'd look at the economics of this design and decide if it has merit.  From an installer point of view, on one hand I have the additional expense of 4 items: a Honeywell control valve, a 24 hr time switch, a pressure regulator, and an automatic air vent.  On the other hand I don't have the expense of a pressure bladder tank, or a purge control center (but I do have a Grundfos pump in the attic and 2" HDPE purge ports outside in the lawn).

In my case I've not ever had the need for a maintenance call for repurging the loop (4.5 years old), or for that matter, any maintenance on the loop.  And occasionally when I measure my static pressure (via the PT port) it's always around 60 psi (regardless of time of year).

I think the summary question is, do I have a water loop design that's less expensive to install and with less benefit to the customer, or is it a more expensive to install loop design with (unknown-to-me) more customer benefit, or, is it the best of both worlds: less expensive to the installer and more benefit to the customer.

Interesting subject.

Best regards,

Bill

Posted By strawmyers on 30 Dec 2011 01:37 PM

Would "pre stretching" the loop eliminate or improve this as a potential issue?  The installer who is recommending the pressurized system said they pressurize the loop to 150psi to take the elasticity out of the HDPE.  He stated that, by doing this, it eliminates the need to go back later and modify fluid level.  Sound reasonable?

This is not standard procedure by any means. I know lots of installers and none of them do this.  I don't see the logic here at all.

Bill,

Over the last five years I have seen the commercial designs get more and more complex with more bells and whistles. The bells and whistles add more expense to be sure. There are allways installers that have the perception that a residential system that emulates a commercial design is better than one that serves the customer. On residential projects we shoot for the highest quality parts installed in a workmanlike manner that is the most cost effective to the consumer= a much lower install price than others.

That being said at the end of the day if the system performs as promised without any frequent maintanance, nothing is wrong with the design or the choices the installer made for his client. I am a big fan of the kiss principle but others prefer other methods, see above.

The advantage we have on forums like this is to get exposed to the largest cross section of differing installs that all work.
Eric

Posted By strawmyers on 30 Dec 2011 01:37 PM

Posted By docjenser on 29 Dec 2011 08:34 PM
Non pressurized systems are essentially call back eliminators. There is a physical reason for that.
After you purge all the air out at startup, you pressurize the system. In A/C you now heat up the loop, causing the plastic to expand and causing the pressure to drop significantly. Due to that drop in pressure, gases, which had been dissolved in the Water (including Oxygen) do now participate out, forming "Air" bubbles in the pipes, which haveno where to go, make noise, can air-lock a loop circuit, and erode and damage pumps. In the past, contractors frequently had to come back and purge out again the loop.
The non pressurized flow centers purge out the mircro bubbles and replenish the water volume automatically, thus no need to come back for air purging.

Would "pre stretching" the loop eliminate or improve this as a potential issue?  The installer who is recommending the pressurized system said they pressurize the loop to 150psi to take the elasticity out of the HDPE.  He stated that, by doing this, it eliminates the need to go back later and modify fluid level.  Sound reasonable?

The pipe will still expand or contract due to 30 F EWT in the winter, and 65F EWT in the summer (in my climate), no matter how much you pre-stretch. I don't see much downsides to non-pressurized systems, and they solve the problem elegantly. Yes, bladders, solenoid valves on timers, bladder tank etc. All try to solve the inherent problem. Plus, if you should ever get some bubbles forming, they simply purge them out. Touch to beat that.