Pump VSD control without a pressure sensor

[tabarouette]

Hello,
I have a building with hydronic radiant floor heating. Each floor loop is balanced for equal pressure drop and has a control valve and goes back to a manifold which wich serves 3 to 6 floor loops (depending on the manifold). Each manifold has a pump with a VSD but there are no pressure sensors with which to control the VSDs.

The control valves for the floor loops are two position valves and open and close based on a call for heating from zone thermostats. Currently, the speeds for the VSD are set directly proportional to the amount of control valves that are open. So if the manifold has 4 loops and only two of them have control valves that are open, the VSD will run at 50%. This doesn't seem right to me since the head produced by the pump will drop off significantly and the floor loops which are calling for heat will get choked off, correct?

Is there any way to figure out the proper VSD speeds to set at part load conditions without a pressure sensor? Would the best strategy be to just set it to run at 100% speed when any floor loop control valve is open?

Thanks,
JR

 

[EnergyProfessional]

GMcD: the concrete has the fibers mixed in, so no rebar or mesh to attach tubes to. If it would have been a metal mesh, I'm not sure that would have been elevated enough. typically those are very low.
the concrete was installed before the partition walls. There is no tubing under the partition walls, but it probably always is a good idea to stay a bit lower since someone will drill a hole to attach frames or other things.

Fluid temp is 105°F (it is geothermal and the limit of the heatpumps... and it probably isn't good for the concrete expansion to heat it too much. Originally the design called for 6" spacing at perimeter and 9" spacing in center. however, during submittal review we got cheated in that the designers allowed a 12"o.c. layout, reducing heat capacity and make the slab react even slower.