Progress... My HVAC company contracted w/ a new more experienced technician. He examined system, replaced my broken desuperheater control board and that is working again. He measured glycol concentration w/a refractometer: it came up 11%. So they rolled in the flush cart and glycol and then read the glycol container and blinked because they claim their glycol has additional additives that indicate 11% should be sufficient for the freeze protection down to 15 deg F. I was surprised. Is this accurate? -- So we watched the system in stage 2 for 3 hours. After ~2 hours, the entering water temp was 30.5 deg F. At 2.5 hours it was 29.6. At 3 hours it was 29.3 and at 3.25 hr it was 29.2. The design point for the loop was 30 deg F. So we were thinking this is not a good behavior. This seems too correlate with the system shutting itself down (freezing out) after ~12 hours on very cold nights. The new tech likes ethanol and it is permitted in Massachusetts so they are going to flush out the glycol and replace it w/25% ethanol. -- They measured the pressure drop across the heat exchanger (and presumably some other factors) and believe we are getting at least 12 gpm with my circulator pump on speed 3. They believe that is sufficient. -- We have a bypass damper to handle the air pressure overload. it is not closing all the way when both zones are calling. Might be something hitting it in the duct. We are tearing that apart next week. The new tech had an interesting proposal to remove the bypass and tie the interrupt the Y2 control unless both zones were calling. The idea being that stage 1 should be fine for 1/2 of a colonial house. And we'd only need stage 2 (full four tons) when two zones were calling. Not sure if I want to try that. -- Thanks for your comments! You guys gave me some helpful context for the discussion with the team!

I'm not sure that a loop that runs at 29*F after 3+ continuous hours of operation is faulty.

I dislike bypass dampers that route air right back to return - result is excessive power / refrigerant pressure and reduced efficiency in winter and potential evaporator icing in summer. A barometric bypass that dumps into the larger zone box or a 2 story foyer is a better option.

I like the idea of dropping down to Y1 if just one zone is calling...in fact it is barking mad to operate Y2 when just one zone is calling.

Well a drop of (30.5-29.3)= 1.2 degrees/hour. 1.2 deg/hr x 12 hours = 14.4 degree drop and that is a frozen loop. The temperature drop might not be linear; I don't know. At least that sure looks like it'll hit the low temp cutoff for the FP1 sensor. That's why I'm so curious about the kind of glycol they were using with these "special additives" and the "low" 11% refractometer reading we observed. And from what I've been reading the glycol gets harder to pump the colder it gets so I might not get the 12gpm they require at these very low temps.

The tech said that the 142 ft/ton of well that we have is not atypical. He didn't think we were underlooped. The driller is widely viewed as the best around. Possibly I have some voids in my thermal grout? We did have a some water at the last 10ft of the wells so you'd think that would help?

I would have thought there would be more margin in the safety design to prevent the system from freezing up as it has been on the coldest nights.

Thanks for your vote for the "no Y2 if one zone" idea.

Posted By m9999 on 03 Mar 2011 11:32 PM
Well a drop of (30.5-29.3)= 1.2 degrees/hour. 1.2 deg/hr x 12 hours = 14.4 degree drop and that is a frozen loop. The temperature drop might not be linear;

You are right, the drop will not be linear.   You really need to graph it over time to see what is going on.

I like the focus on antifreeze and am also not convinced there is any other loop problem.
I also like Y2 interuption, you could use a zone panel that "bleeds" as well. Weighted dampers are not a good fit with ECM blowers.
Sounds like new tech is a pro.
It might be interesting to have his perspective if you could get him to contribute to this thread.
Joe

I have a bypass damper and there is some question if my ducts are sized properly for when only one zone is calling. I was wondering if it would make more sense to just keep it simple and force both zones open always. If either thermostat calls, then we'll heat (or cool) both zones. Why send conditioned air around the bypass loop between the supply & return?

If we interrupt Y2 as my new tech suggests, I suspect we'd want to interrupt W as well (or force both zones open if either is calling for W). That seems like it is getting more complicated.

Sounds like a typical "using the wrong glycol antifreeze" problem. Some of the brands do not contain 100% glycol, the additives usually do not add freeze protection. Do a search, we widely discussed the problem. EWT going down to 29F and the dynamics you describe are normal, your loop appears to be fine, and you have more than enough flow. Fix the antifreeze problem first, that way your system does not go into lockdown anymore.

Yeah, we flushed out the glycol and put in 25% ethanol -- a mix called geosafe see http://www.houghton.com/fluids/geosafe/index.html

We are using speed 3 of my Bell Gossett circulator and the pressure drop (I'm told) indicates more than 15 gpm.

I ran a 7 hour test last night in stage 2 (with a couple of windows open to keep the house around 72 degrees) and the aux electric heat turned off at the service panel. The EWT started at 39.8 degrees dropped almost linearly for 4 hours. Then after 4hours the loop reached a minimum temp (EWT) of 35.3 degrees and stayed there for 3 hours. I think the problem is solved. (I was measuring the temp with a sensor zip-tied to the outside the pipe at the GSHP, so it is not 100% accurate, but whenever we compared with the temp observed by the tech using the P/T port , it was usually within 1 degree).

When we were going to keep trying the glycol last week. The glycol they brought (which they claim is the only glycol they ever use) had a big pink sticker on the top that said the additives provided additional freeze protection with a chart showing how much one would need of their product for freeze protection. And for that label the 12% reading we saw on the refractometer seemed appropriate. I can try to find the brand name but I don't care so much about that now that my loop is behaving better. Maybe we got a bad batch of glycol when first installed the system. Maybe the sticker is not telling the truth... I don't know.

Now to figure out what to do with all this extra air flying around my bypass & with my too-small duct work.

indicates more than 15 gpm

I would dial back the pump some..... you should only be pushing around 12 GPM. Excessive water flow will cause premature heat exchanger erosion.