? on snow melt

Blackoakbob

a typical beginning....it worked okay last year statement. I have a system that is just slow to poorly operating. The flat plate hx has a 36 degree drop across it and the boiler modulates at 50% to 55% with a outlet temp of 146 and return of 110. It just seems sluggish. There was a question of the anti freeze possibly gelling but with the td across the hx it would seem I have flow.I had a problem earlier with the home heating side of the system but that has been resolved...the expansion tank was too small. Any tips would be appreciated Best regards and Happy New Year to all.

Mark Eatherton

The LOAD side of the HXer....

is where you are supposed to be seeing 140 degree F water, not the boiler side.

Also, check the operating pressures on the load side of the system. WIth viscous fluids, NPSH becomes even more critical. If the pressure gets too low, the pump may struggle moving cold, thick fluids.

THere is also a possibility of bacterial fowling of the FPHX, which affects not only flow, but also heat transfer.

ME

Blackoakbob

pressure....

thanks for the reply, Mark. I do a have 20psi on at the inlet to the pump and at the manifold outlet to the slab, possibly 22 psi, and the temp on the load side never gets over 70 degrees from an inlet temp of 20. I know from my gshp systems that you need to keep the pressure up there. It looks like it's time to take things apart and see if the hx is fouled. We have had an above average December for snow so this has been agravating to say the least. Best regards.

troy_8

Snowmelt

I set my snowmelt supply setpoint at 130 deg. If you are seeing the max supply at 70deg. with a 50deg. drop it indicates a need for cleaning the heat exchanger. I usually see about a 30deg. td between supply and return.

Kal Row

flow!! flow!! flow!!...

if your flat plate is in line with the snowmelt loops, then "fogedaboweet"

you need to move that antifreeze mix at high speed in order for it to melt evenly without cracking you slab

so it’s three pumps solution
1 boiler to hx
2 hx to snowmelt loop injected in close t fashion
3 snowmelt loop itself

and you always need to put strainers on both sides of any flat plate hx or it becomes useless in short order – it’s a lot simpler to blow down a strainer than to remove and reverse the flow through the hx to get the dirt out of
the fine inter-plate holes

just run the return water from the slab into a white 5gal bucket and look at the junk in there - had a snowmelt fill job the other day, that had ice plugs in some of the pex loops from construction site water and had to wait until the adjacent loops heated the slab enough to get the antifreeze though the plugs, and trust me, if there is construction site water in there, then there is dirt in there too!!!

see attached pdf

Blackoakbob

Thanks for the replies...

I appreciate the kind input,I can see the value of the injection piping scheme and that may well be the solution if it has to come apart anyway. Best regards,