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Green Building Bible, Fourth Edition
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    • CommentAuthorrevor
    • CommentTime5 days ago
     
    Commissioning my u/f heating mainly to condition the floors by increasing temperature gradually. Having difficulty achieving full spec on flow rates on the loops requiring a high flow rate. The store is open vented direct heated from a boiler and has solar thermal panels feeding it. I though (naively as it may now be the case) that the manifold pump would circulate the water from the T/S and it does for most of the lops that require anything below 2.5 l/min. The manifold temperatures required are met and the floor heats up and after a day running the floor temperature is the same as the loop return on all loops .So everything is working apart from flow on some loops.
    The mixer unit between the manifolds is by Ivar and from looking at a short video on their web site it looks like the supply to the manifold mixer valve needs to be pumped. It is set up with bypass valves to control the return temperature to the" boiler" which should be hotter than the return temperature of the u/f heating loops but in my case it is not as the return to the store is the same temperature as the loops. Has anyone done a set up driving u/f from a thermal store and if so how was it configured.
    • CommentAuthorCWatters
    • CommentTime4 days ago edited
     
    My system is similar to yours.

    Some preassembled manifolds are designed to bolt into an existing rad system without TS and have a bypass on them where the boiler flow and return connect. This is intended to allow the boiler pump to continue to circulate water to the rads when the UFH mixer is fully recirculating.

    If this type is used with a thermal store and no rads they need a pump to circulate water from the store to the manifold and back.

    Personally I feel this is a mistake, not least because it stirs the store. Other manifolds don't have a bypass and can use the loop pump to draw water from the store through the mixer.

    My builder purchased this type of manifold and I was going to remove the bypass instead of using a pump but he was worried about the warranty pressed me to fit a pump. I fully intended to remove the pump and bypass some day but never got around to it.
  1.  
    Revor, if I understand your description correctly...

    - UFH manifold fed by pump located immed after mixing valve.
    - flow from and return to therm store, no UFH linkage to boiler
    - your problem is that you aren't getting the flow rates to certain loops.

    Are you looking at the case where ALL loops are being fed at the same time, or is the low flow on loops when only that loop is open (ie. is it a pressure drop issue on one or two loops, or a total flow volume issue)?

    By the way (an not to do with flow rates) have you fitted a high temp switch, which will shut off the pump in the case of excessive water temp feeding to the manifold. Lots of people are completely unaware of this building regs requirement, as it sits in a separate guidance document.
    • CommentAuthorCWatters
    • CommentTime3 days ago edited
     
    It is set up with bypass valves to control the return temperature to the" boiler" which should be hotter than the return temperature of the u/f heating loops but in my case it is not as the return to the store is the same temperature as the loops.



    Did you mean a bypass or is there also a mixer to control the return temperature? I have such s mixer on the primary side of my store to control the boiler return temperature. As I recall Grant say this must be >40C for their oil boilers.
    • CommentAuthorrevor
    • CommentTime3 days ago
     
    Thanks for all the inputs. I'll respond to the comments as a whole.
    The manifold pump is part of the mixing assembly and sit on top of it. The flow from the store comes in via an on/off valve controlled by the manifold control system so when a room calls for heat this opens and pump starts and the zone valve calling for heat opens. The manifold temperature is controlled via thermostatic valve set to the required temperature and sensor is wired into the flow manifold. The manifold temperature can be monitored by a dial gauge on the inlet to the flow manifold there is also a sensor on the junction of the pump outlet which is wired into the manifold controller. I think this is associated with the controller dip switches which can be set to 30 45 and 60 degrees to allow for commissioning the floor screed and presumably acts as max temp controllers.
    Within the mixer assembly are 2 bypass valves. The main one primary bypass controls the amount of water going back on the return leg to the heat source. The amount of opening depends on the boiler requirements for "optimal performance" I have it set at fully closed as it came from the supplier (Robbens) if I open it the temperature drops as water flows back to the boiler/store. I was advised by Robbens technical that the system needs to have a pumped supply which would be the norm for this manifold assembly and suggested I may be able to overcome the lack of a pumped supply by adjusting the bypass valves. The secondary bypass is a needle valve for adjustment of the water from the return manifold entering the mixer. Playing around with these setting does not improve matters. I am uncertain as to what this valve does when closed does it send to mixer or back to the store.
    As mentioned initially I can get the system to work but cannot get the flows on the high flow rate loops which are the longest at 100 t0 110 m. The flow does drop slightly on the non achievable required flows when all zones are calling for heat. One of the loops is only 30 M and close to the manifold its requirement is only 0.6 l/min but I can get a flow rate well in excess of the requirement (3.5 l/m) of the non performing loops so I suspect that there is not enough supply going to the manifold to overcome the frictional effects of the longer loops.
    The solution I think is to fit a pump from the TS to the manifold I am not that concerned about disturbing the stratification it would help. I think it may be a v big ask for the circ pump to heat 180 sq M via 1090 M of pipework in 12 loops. when it comes to commissioning upstairs I may not need the assistance of a pump as gravity will be with me. The flow to upstairs rises and returns from the store directly to the manifold with minimal horizontal pipework.
    Without the boiler on and not flowing water through the store I can due to the position of the heating draw off outlet on the store soon run out of useable heat as the store temperature at the top gets hotter and the heat draw off gets cooler. Just turning the boiler on and before producing any useable heat from it, the heating draw off temperature has risen considerably as the hotter water gets drawn down. I append photo. 1 Inlet valve 2. thermostatic valve 3 dial gauge 4 primary by pass 5 secondary bypass 6 return to heat source.
      DSC_0015_LI sized.jpg
  2.  
    My usual caveat on responses here is that this is my understanding, based upon your interpretation, so obviously without seeing the installation, there's an element of uncertainty, but here's my thoughts...

    1. you're right to keep the bypass from flow to return closed, as you're not linked to the boiler, so def do not want bypass back to the TS. This is one of the reasons I normally include TS's in my designs, so there's no link between needing UFH, and the heat source having to run (stops short cycling, amongst other things etc)

    2. "sounds" like you have dual temp control for the feed water, ie. safety over ride in case of the TMV failure.

    3. I'm not clear (like you) why there is a needle valve to control the cool return water flow rate into the TMV, as I would expect the TMV to control how much cool return it allows to mix with the hot feed, since that's what delivers the set temp. May be worth asking Robbens to explain exactly what that valve is for, and for what circumstances.

    4. Makes sense that the flow rate of the long (non-achieving) loops will drop a bit, as you open up all the other valves, since that's a function of the pump curve, (increased flow, reduced head)

    5. speaking of pump curves, I can't quite read the pump label, but it looks like an Alpha 2L, not sure if it's a 50 or 60? This has various settings for pump performance. If you set it to "III" for the moment, that will give constant speed, and so the highest possible flow rate for any given pressure.

    6. The pump's pressure will be determined by the index leg, or the loop with the highest pressure drop, likely to be the longest loop. That then fixes the max poss flow rate from the pump. It's not really the total length of pipe, since the loops are in parallel. Make sure the adjustable valve on this leg of the manifold is fully open. From memory, you can alter that at the brass body under the little black plastic flow setter. In other words, you can do a gross adjustment at the brass body, then fine tune that with the black plastic twiddler. You need to make sure for that index loop, and any other loops very close in length, that you have the minimum possible resistance at that flow setting point. Sometimes the factory set position is a middle point.

    7. If you have ascertained that the longest loops/loops are now at the least pressure drop possible for that length of loop, and the flow rate still is not adequate, then you may well have to add another pump in series to augment the loop pressure. How far away from the stipulated flow rate for these couple of long loops is the actual? Do you know that it will in fact be inadequate to keep that/those rooms warm in winter? Calculations of flow rates and heat loss, and heat requirement are subject to many influences, not least of which people adding in lots of insurance by way of conservative numbers, which can add up to implying you need a lot more flow than you actually do.

    8. Gravity doesn't have any effect in a closed loop, since what goes up, must come down. It's only the additional length of pipe, that would then caused a pressure drop. I don't understand your comment about water rising upstairs. Are there UFH loops upstairs? Do they come off this grnd flr manifold?

    9. You mention you very quickly run out of heat in the TS in the zone that the UFH draws from. What is the Total volume of the TS, and what volume is between the UFH flow and return connections? It does make sense that when the UFH first calls for heat from the TS, say in the morning when the night set back flips to morning room temp setting, the water in the loops will be cool, so there's a sudden large surge of cool water returning to the TS, to it will take a while for the TS to catch up. The volume questions above will say more about that. Also make sense that when the boiler pump starts running, it initially destratifies the TS, as the flow is likely in to the high point on the TS, and the return near the base, so it pushes hotter (normally DHW) water, down the store towards the boiler return connection, which is also down towards the UFH flow connection.

    Hope there's something in all that which helps. :confused:
    • CommentAuthorCWatters
    • CommentTime2 days ago
     
    Still looks similar to my system in operation. Pretty sure with that design you need a pump controlled by same signal as valve 1.

    The mixer 2 controls the flow temperature to the floor loops. It blends a variable amount of hot water from the TS with cold(er) water returning from the floor loops. Depending on the mixing ratio there will be some water returning from the floor loops that isn't used by the mixer. This excess is returned to the TS through 6.

    When the floor temperature is up to temperature or too hot the mixer 2 recirculates most of the water in the loops and takes very little new hot water from the store. In that condition a new pump on the TS would be blocked if it wasn't for the bypass from 1 to 6. Might be worth looking at a grundfoss alpha pump that regulates its flow but ask the Manifold supplier what they recommend.
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