Taco circulator pump losing pressure

Boston83

Hi everyone, 
trying to figure out why our rooftop 30hp Taco pump that supplys a closed loop 100,000sqft office building to lose its pressure when the weather starts to turn cold. It’s normally at 20psi but once the cold weather comes it decreases to 10. 

Then I feel like I need to add more water into the system. If there was a leak I’d think I’d notice it dripping from ceiling. We do sometimes need to flush the a heatpump cuz of metal flakes in strainer. And we also change the filter feed sock each month so maybe that’s letting air in ?
The expansion tank is before the pump. Maybe the seals need to be replaced again? It’s not leaking. I’ve noticed the joints where the black iron pipes connect are creating white flaky residue. (35%Glycol system)
thanks in advance for any help or ideas. 

Mike

pedmec

where are you measuring? circulator suction/discharge or somewhere else.

are you measuring with system operating or static.

what is the fluid being used for? hot water, chilled water, or condenser water.

need some info

Boston83

this guage is a constant 40
which is normal I was told but (2nd pic) guage is what fluctuates when the temp drops. 

Boston83

Boston83

This is for a closed loop water source heat pump system and BAC cooling tower. 

Boston83

5 caravan slant fin boilers for heating the loop 

Boston83

pedmec

are you maintaining the same loop temperature in the winter as you are in the summer?

Boston83

During the summer time loop temp is between 82-86
winter is ranges from 70-78 depending when the boilers turn on to heat. Morning time it’s lower but as the day progresses the loop temp climbs. 

I shut down (drain) cooling tower once we hit freezing temps. And if needed the low fan suffices. 

Zman

When I have seen that happen it was caused by air trapped in an air handler somewhere in the system. When the valve to that air handler opens, the system sees that air pocket as a second PONPC (expansion tank) and the pressures get whacky. Generally, the suction side gauge should be pretty steady (sometimes a bit higher as system temp rises) and the discharge side will move around a bit if the circulators are variable speed as it looks like yours are.

pedmec

Temperature in a closed loop system will change the pressure in relation to the temperature change. In a water source heat pump system the system design parameters are between 65-95 depending on the engineer (some i have seen designed between 60-90). In the summer you could be operating on the higher end of the temperature range depending on how fast the heat of rejection is happening which would increase the system pressure. While in the winter you will maintain the design temperature by adding the boiler to the circuit.

Having said that you could also have a water logged expansion tank. Due to the possible temperature difference from summer and winter If the tank(s) are low on air then it will exacerbate the situation as the ability to handle the change in expansion will be less. You will have to isolate the expansion tank and drain it before measuring.

Boston83

Awesome, thank you for all your insightful information. I really appreciate it. 

Boston83

Just for my knowledge. Any thing bad will happen if I don’t take care of this asap?