Geothermal system with WSHP’s

[Mr. Nobody]

Alright guys here is the problem... I have an 80,000 square-feet two-story building that has 21 water source heat pumps. The last four units in the building are located at the end of the geothermal loop, these units trip out on high head pressure every single time the ambient air temperature reaches the mid 90s. I have checked and cleaned all y-strainers and even have pulled multiple circuit setters to clean as well. I have had this problem consistently for the past couple of years when the summer temperatures get high. I have heard that this facility has a geothermal loop that is too small, however, there is also a supplementary cooling tower. The reliable controls interface shows that the water temp is 89/98 in the heat of the day. I also get the same readings when I check the water temp manually. This facility has a history of running high head pressure throughout the entire building. However, the only units that I cannot keep the head pressure down enough on is those that are located at the end of the loop. I’m confident that I don’t have any water restrictions at the units. Also, the loop has a water treatment system on it. Suggestions?

[Firefighter34]

High head pressure can be a couple different things, if the ambient air is very hot it can cause high head pressures. It could also be low water flow. But by the way it sounds is it is tripping off on high head pressure because of a combination of things. The hot ambient air and the unit being on the end of the loop not getting the correct flow is more then likely causing the problem. When you say the water temp is 89/98 is that the load side water or the source side of the unit?? I would need more information to help you with what's going on. I would start with taking source side delta t and the pressure drop on the units when they are running on a hot day.

[heatingman]

You have circuit setters. They have ports on them. Order a read out probe set, and get a decent analog gauge maybe 0-50 psi, at least 4.5” dial size.

Measure the pressure on both sides of the circuit setter. Take the difference in pressure and multiply by 2.3

That will be your pressure drop in feet.

With that number, and the setting of the circuit setter you can find flow rate.

Assuming its a Bell and Gossett setter, you can download there system syzer app and just plug in the numbers.


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[servicefitter]

What is the outside temp and water temps. Has anyone put flow meter on the four units? Cleaned the strainer, checked design flow of pumps? Is there a heat exchanger and has it been cleaned? Loop temps using the same thermometer? Have a set of prints?

[lukieo]

I have a very similar situation at a facility i work out. I've found that many times the techs before me have adjusted the charge before verifying flows. winter time low suction must add gas mentality when really it's restricted flow and a dirty filter. You may need to head the route of pulling the charge and weighing it in if you have proven flow yourself and are still having problems.

[Cool breeze 38]

if its just the 4 at the end of the loop its water flow. Have you checked the flow at each balancing valve to make sure you're not over feeding the closer units and starving the furthest.
Have you checked what the total gpm of the loop pump it? It is sufficient? you may not have a restriction, but just not enough gpm.

Do you know what the wetbulb is on these hot days? Is the tower 25% or? of the total system and what is it set at.

[buford]

Any previous TAB done? Might be a good place to start if not.

[71CHOPS]

Any previous TAB done? Might be a good place to start if not.

That’s the ticket!!

When I have problems like this, the very first thing I want to see is the original blueprints. You need to know what all the building design conditions and specs are supposed to be, then locate the TAB reports that tell you the actual original system operating conditions.

Once you have that information, you can begin to troubleshoot the entire system.

[servicefitter]

Most systems use auto flow circuit setters calibrated to a certain flow rate and are they the correct ones for the units. Problems come from fwo things bad water treatment / glycol has turned to p**p or dirty system that has to be cleaned by a external bag filter and strainer cleanings. Have you pulled main pump strainers? Have looked at shut off pressure of the main pumps and their curve. Someone close the triple duty valve? You need the mech prints.

[Juan Madera]

...and probably not plumbed reverse return either.

[joe_arsenal]

90 supply is pretty high for wshp. I know the manuals for most brands show operating temps 50-90 but you do have geo wshp’s which lowers the safety trip temps. All my buildings with geo wshp need 80 supply water or less to keep going. Also found many “additional” heatpumps added after remodels and such, I had to jack the closed loop pressure up 2 psi to get enough flow so everyone was happy. Maybe the wrong way to go about it but it worked in those two buildings. Can a more experienced tech chime in? I’d love to learn more! I spend most of my time in high rises with wshp.

[servicefitter]

Do you have a closed circuit tower or open tower with a plate heat exchange need temps in and out. Nevered answered my question about water quality and the stainers.