Balancing two manifold setup problem....

[cplev]

Hi all 

 

First posting here. I could do with some advice on a rather ad hoc ufh system !

 

We planned and built our house some twenty years ago - it is an four bed detached house, with an oak frame clad in SIP panels, so a reasonably high level of insulation and airtightness, but with a very open interior aspect. We designed the underfloor system which serves both the lower and upper floors around a dual circuit Geminox boiler which had a wide modulating range and used weather compensation, varying the flow temperature and using the boiler pump rather than using a blending valve and pump set. We followed the principle that a high delta T plus modulation and weather compensation would deliver the correct amount of heat at the right time.  However the layout of the house meant that we had to use two manifolds, one on each side of the house rather than running multiple long loops back and forth - the open aspect of the design meant quite restricted space within the fabric of the structure for the pipes and other services. Each manifold serves a number of rooms which are individually zoned and controlled with Heatmiser stats back to a wiring centre controller and the usual actuator valves, some with multiple loops to cope with the different floor areas. However no flow valves were fitted to the manifolds at the time. This article reflects our thinking at the time: https://modbs.co.uk/news/archivestory.php/aid/1499/Modulating_boilers_are_ideal_partners_for_underfloor_heating.html

 

The system has worked reasonably well up until now with the caveat below. Recently though we had to replace the Geminox and did so with a Viessmann 200-W. An increased flow temperature led to an overall improvement in comfort but showed up some shortcomings in our original ideas and design of the system.

 

One manifold is sited within 2m of the boiler whereas the other is around 18-20m away. Seemingly as a result the loops fed by the second manifold seem to underperform, presumably due to system resistance, and I have been considering what steps to take to address this. Firstly I have changed the manifolds to a set which has flow valves and have also installed Salus auto balancing actuators to even out the differences in return temperature from the individual loops - the system was never balanced properly in the first place!

 

However I don't think this modification is going to address the lower flow rates from the second manifold, which seem inadequate. Floors fed from the second manifold are noticeably cooler due to the lower flow rate. What steps might be advisable to better balance the flow to each manifold from the boiler? I have followed many conversations on here and thought about retro-installing a pump set to each manifold to relieve the boiler pump of some of the load, but I'm not sure if this is the right way to approach the problem. One of the discussions in this forum is about the need(or not) for a blending valve and thermostatic control to limit the flow temperature but there is a strong argument for no blending required for ASHP systems; this also seems to apply to dedicated circuits from a modulating gas boiler with electronic control of flow temperature like the Viessmann.

 

Can anyone comment or suggest a way of improving the flow rate to the second manifold?

Is installing a pump set at each manifold the best way to do this?

Is a low loss header needed?

Are the Salus valves the best way of balancing the loops - I think they are based on a 7 degree temperature difference - perhaps this is going against the principle of a higher Delta T?

Any help and comment is appreciated!

 

Chris

 

[LA3222]

Seems simple to me.

 

First manifold is next to boiler and the pump in that's pushes the flow around those loops.

 

Next manifold, the pump has to pish the water 18m before it then has to also pish it around the loops. A lot of work.

 

Pump a pump in to do the leg work for that manifold.

 

I have two manifolds, both have their own pumps. I have a third pump which pulls from the buffer tank/pushes it to the manifolds. No issues with flow.

[cplev]

Might another option be to use a DRV valve on the shorter of the two manifold legs from the boiler to achieve a better balance between the two?

 

Chris

 

[Temp]

Perhaps replace the existing pump with two, each feeding just one manifold.