Bard geothermal quiz for you old timers
Today I met an old time farmer who has a Bard water source split system heat pump. He told me his heat pump never has worked right since day one. He said he's had numerous service technicians work on the unit every year for the past 11 years trying to get it to work properly.
I immediately noticed that the txv was iced up and could tell it was starving for r-22. My suction pressure was 20 psi and the compressor was cycling on the low pressure switch. My inlet water temp was 50 degrees and the outlet temp was 49 degrees. (water was SCREAMING through the exchanger). I glanced to the TXV and noticed that it had been replaced less than a year ago (dated). Naturally my first thought was it was simply low on charge. To be thorough, I switched to cooling.
Initially the suction pressure stabilized at 40 psi and the high side was 125 psi. A quick glance to the indoor unit to see a piston style meetering device. I mumbled "well thats not too far off.." I decided to elevate the high side pressure by closing a valve on the water supply to see if the suction pressure would come up. I was suprised to see that while my suction pressure initially increased, eventually it FELL below 25 psi. "must be low on charge.." I said for my benefit. I wanted to add charge in the heating mode so I de-energized the RV, opened the water valve and went to get the refrigerant.
I got back to the unit, new 30 pounder and scales in hand. Low and behold the suction pressure was up around 45 psi. "What the..." I said under my breath. The old timer was looking at me with his hands on his hips. I looked into his face and I could see the impatience that so many others must have seen. "Do you know how many bottles I've seen out here?" as he hastily pointed around. I managed a small laugh as my eyes darted around the internal components. I decided to watch things for a few more minutes. Eventually the suction and discharge pressures began to fall and the txv began to ice up. "There it goes again.." I mumbled. The heat pump fell back into the cycling on the low pressure switch as 51 degree well water fed by a 2HP irrigation pump screamed through the exchanger at mach speed.
This is a very simple water source split system heat pump with a remote desuperheater serving the domestic HWH. The water source is an ungodly 2hp pump at 70 psi feeding the exchanger via 1 1/2" pvc. The inlet water temperature is 51 degrees. The system has the correct charge as per nameplate. Both the heating and cooling cycles operate at normal pressures for 10 min or so before the pressures go foul. There is no debris or moisture in the system causing meetering device failure.
The old timer is tired of hearing the heat pump run continuously, the massive water pump cycling every 10 seconds, the auxillary heat light on and paying the utility company his social security check every month.
Whoever can figure this out gets a new bottle of POE oil in there stocking.
Last edited by crmont; 12-14-2007 at 02:16 AM.
Reason: added "or moisture"
if memorie serves correct first this is to slow the water flo down to about 12 to 14 gpm. The check your air flo very inportant as we all know
check the water coil for any posible restrictions
high side sould be arround 250 to 275 with 12 to 14 gpm
low side should be arround 50 to 60 in heat and about 50 to 70 in cool
like i said if momorie servse right
the txv icing imo is from not enough stransfer of heat because the water is going through to fast
that's what I was gonna say 1 degree differential is not enough. pumps probably too large.
Originally Posted by tinknocker service tech
You can't fix stupid
Definitely slow the water down, small ones I've worked with, 3-5 ton units only required 6 to 8 gpm with 3/4" water lines, more than that was asking for trouble.
High pressure with R-22 should be in the 225-250psig range with proper waterflow. Low pressures depend on load.
Generally Bard water source units will last for a very long time, the usual refrigerant leak spots will be in the water coil and/or evaporator coil.
Two things are infinite: the universe and human stupidity; and Im not sure about the universe. Albert Einstein
I have the same thoughts. Too much water.
Karst means cave. So, I search for caves.
The problem exists in heating or cooling. Slowing the water in heating mode does not elevate the head pressure. You might wan't to read the first post again.
Although there is no need for the quanity of water I agree that it should be slowed down.
I think I would have the same thoughts that you had, sounds like moisture or floating debris is in the system causing a restriction at the metering devices or a low charge.
I would probabley recover the charge, cut the liquid line blow out liquid line with n2, add bifllow drier, evacuate and weigh in the correct charge of fresh refrigerant.
good luck iso
I never let schooling interfere with my education... Mark Twain
Slowing the water in the heat mode (below normal GPM) will lower your suction pressure and in turn will lower the head pressure. Now, slowing the water in cool mode will increase the head pressure.
Originally Posted by crmont
Karst means cave. So, I search for caves.
Is there a possibility that the water loop pipe is actually too, large, at 1.5", such that there isn't enough water turbulence, and thus not enough heat extraction/rejection to/from the water?
Exactly. If you read my initial post, this is what i did.
Originally Posted by karsthuntr
This is a great guess but remember this is not a geothermal HP with a fractional HP pump. Water flow is definitely not the problem. I agree that too much water in cooling mode might create too low of a head pressure, but I have already elimiated this as an issue. In heating mode (open source don't forget) you can never really have too much water flow becouse the heat source is unlimited, however it is a comlete waste of energy and water.
Originally Posted by a0128958
Definitely a sound statement, however numerous technicians (well at least two) tried this exact course of action with no results. The last tech replaced the heating txv less than a year ago. The old man called him back complaining about the cycling compressor and the tech said and I quote "Just switch it over to cooling for 5 minutes or so then back to heating. That should fix it for a while.." No kidding.
Originally Posted by ISOTHERMAL
Sounds like a defective bypass valve in the water loop that was installed to control the water temp.