Radiant system feedback needed

Jason Quinn

I went to see a completed radiant system installed in a new house that is underperforming. There is a Weil Mclain CG-7 installed (200,000 btu input) serving (2) radiant zones- (1) on the 1st floor and (1) in the cellar. The house measures 18x60 and has spray foam insulation. I have yet to do a detailed heat loss calc, but I believe heat loss for each floor is 20,000 btu or less. Both zones installed in 4 inch concrete overpour, 12 inch on center, insulation underneathe and have the same marble floor covering. **These install details were given to me by the owner. There is no mixing device aside from a 3/4 inch supply-return bypass line operated by a ball valve which serves as boiler protection. Also "manifolds" do not allow for circuit balancing or purging and need air vents too.



On the first floor there is only 3 pex circuits tied into each manifold. Owner says installer divided space evenly into 3 loops aside from leader length. Only (1) loop gets hot and each zone pumped by a 007. By my calcs, there is at least (1) 500ft loop of 1/2 inch pex. This exceeds the 007 pump capacity so there is a flow problem.



I will also note that the t-stats and pumps were wired "backwards". So on a call for heat flow was induced in the "other" zone. That, at least, has been corrected



Please give me feedback as to what you would prioritize to owner as a fix and possibly establish a minimum requirement of work before getting involved. I have grappled with a few potential solutions:



1. At a minimum, replace pumps with 00R or 15-58 ( or the proper pump to attempt to achieve a 10 degree delta t) and re-do manifolds to allow for balancing, purging and air venting.



2. Do #1 and add a mircrobubble resorber and mixing with boiler protection. Please give feedback on preference of 4 way valve or variable speed injection pump



3. Do #1 and #2 and add a buffer tank



4. Consider flow reversing valve?



5. Replace boiler with appropriately sized modcon, upgrade pumps and manifolds

NRT_Rob

I would

design for 20 degree dt. reduces flow, should be able to make those loops work.

use mixing.. method, don't care. we like 3-ways but you can use a 4 way perhaps.

buffer tank definite in here



compare all of that to a mod/con cut out and replace. don't forget to add at least 20% efficiency benefit to the mod/con... probably 30%. probably will cost justify the decision very soon...

Jason Quinn

Thanks, Rob

for your input. I feel the same way. The modcon makes sense in several ways. It just seems that trying to make the existing oversized unit "work" is throwing good money after bad. I'm going to present this reasoning to the owner and see what he says. Perhaps we can do this upgrade in stages if necessary.

Jason Quinn

Purging the system.... what am I doing wrong?

I installed a new manifold that has isolation valves, auto air vents, circuit setters, temp gauges and hose cocks on both the supply and return manifold. I closed the iso valves and hooked up to street pressure at the supply hose cock and tried to purge each circuit separately through the return hose cock. The problem is I'm not getting any air. From 1 circuit I must have purged approx 40 gallons of water through the system. The only time I got air was when I opened up the return manifold auto air vent; then a lot of air came out. Was the air vent letting air in making me believe it was system air? Are all air vents supposed to be closed when purging? If so, why arent I getting any air out of the system with street pressure and over 60 gallons of water going through each circuit? Please advise.

Gordy

Air vent Venturi effect

Its possible that the air vent was going sub atmospheric pressure due to the high velocity of street pressure water passing by it.



 There may not have been that much if any air in the loops when changing out the manifolds. If one at a time were done the loop water probably did not drain much. Think picking a straw full of water out of a glass with your finger over the end.



That boiler is huge for that house how old is it? I have a CGM 7 from 1993, and it is all most 3 times to big for my 2000 sf ranch with 50's construction heat load is 67000 btus. Good boiler no problems with it except it wont die so I can get a nice firetube mod/con. Things been taking 90 ish return water for the last 18 years with no condensation damage at all. The only thing I can figure is the boiler is so oversized it does not even belch at low return water temps. Simple bypass for the radiant helps to.



Gordy

Jason Quinn

Thanks, Gordy

I didn't consider the possibility of the loops not draining, makes sense though. Anyway, I'm dealing with a 70 degree delta tee even with the 15-58 on speed 3; the supply temp is 160 and return is 90. I guess the loops were longer than anticipated or my calculations wrong. I haven't run the numbers yet, but I'm considering bumping up to a 26-99. The problem is the header is not piped primary secondary and I'm afraid this pump will overpower the cellar pump causing no flow. A header repipe may be in order with some type of mixing device.