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New System Flow Rate

Brly
Brly Member Posts: 5
in Radiant Heating
I just started up a new Thermolec boiler system in my 32x44 shop. Single zone, 6 loops of 1/2" pex in a fully insulated 5" pad. The manifold does not have flow gauges. The Grundfos Alpha1 pump has 3 speeds, I have it set to the lowest and turned down the return manifold valves so that the pump is showing 4 gpm. The temp seems to have stabilized at 90 degrees at the boiler and out going manifold. Return manifold is at 64 degrees. Should I continue to close off the return manifold valves to reduce the gpm and increase the temp? I have a slab sensor and the floor is currently at 52 degrees. New to radiant, just trying to figure it out. Let me know what additional info is needed. 
Thanks,
Ben

Comments

  • Hot_water_fan
    Hot_water_fan Member Posts: 1,840
    edited October 2022
    Should I continue to close off the return manifold valves to reduce the gpm and increase the temp?
    No. To raise floor temp you can raise flow and/or increase the set point. Open the valve fully. As the system runs more, the delta T should close. You’re not yet at steady state, this slab will take a long time to change temperature. 
    Zman
  • Brly
    Brly Member Posts: 5
    Understood. I'm trying to increase the temp going into the floor, aiming for 110 degrees. To do that I need to decrease the flow. Is that correct?
  • Hot_water_fan
    Hot_water_fan Member Posts: 1,840
    edited October 2022
    No, do not decrease flow. The slab heats the most when the average water temperature is highest, which is when supply is closest to return temperature. This happens as flow rate increases. Open the valves :smile:. 
  • Brly
    Brly Member Posts: 5
    So I think you're trying to tell me to just run it wide open until the slab stabilizes and not worry about the temp going into the floor for now?
    Zman
  • Hot_water_fan
    Hot_water_fan Member Posts: 1,840
    edited October 2022
    Correct. You’re heating 30 tons of rock, it’s going to take some time. There’s really no reason to restrict flow here, ever. How big is this boiler? 
    mattmia2
  • hot_rod
    hot_rod Member Posts: 22,120
    The higher the flow rate, the more heat is going into the slab. It could take a day or more to reach the designed for supply temperature

    You are trying to rev up a large concrete flywheel. Keep the circ on speed 3
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    mattmia2
  • Paul Pollets
    Paul Pollets Member Posts: 3,656
    When the slab temp stabilizes, turn the pump speed to "Auto".
  • Brly
    Brly Member Posts: 5
    Thanks for the replies, been out cleaning up leaves all day. Room temp is up to 65, floor temp at 62. Supply manifold is at 80 degrees, return at 68. Its 54 degrees outside right now.
    The boiler is 9 kW, 30,708 BTU. Bought a prefab panel from Blueridge. I'll dig out the paperwork and see what they designed for. I bought the whole system over a year ago when I was pouring the floor so its not very fresh in my mind.
  • GroundUp
    GroundUp Member Posts: 1,907
    The GPM readout on the Alpha is a guess at best. There is little chance it's actually flowing 4 GPM if you've got the valves throttled as you say. Leave them wide open and personally I'd turn the circ to constant speed 2 for that slab. If the temps were 90 and 64 as you stated, GPM is only 2.36. If room temp is 65, the floor can not be 62 and still be heating- the slab temp needs to be higher than air temp in order to be emitting heat to the space.
    Zman
  • Brly
    Brly Member Posts: 5
    The valves aren't throttled, I opened them up this morning per the suggestions above. 

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