PID T-stat

Aidan (UK)

Yes, with 3-phase inverters; much too expensive for this application.

I think there's a Danfoss system which uses a proportional control signal to modulate the valve actuators.

Paul Rohrs_4

PID T-stat and variable speed pump or Delta P circulator

I was enjoying Wayco Wayne's post about being a Circaholic and thinking about the use of circulators instead of zone-valves. My thinking then took me to ∆P differential bypass valves being used with zone valves. The next step would then be to have this differential pressure circulator used as a "zone circulator".

So now, with this grundfos ∆P circulator (available in the US only with the Vitodens (?)), the additional use of the differential bypass will be rendered useless. As zone valves open and close, the ∆P circulator will ramp the flow rate up and down like a variable speed circulator. Fine. Great.

What about zoning with these ∆P circulators and using a T-stat with PID logic? As a zone of radiant floor heat falls below the setpoint and calls for heat, the PID logic in the stat will recognise how far below setpoint it has fallen and will speed up the flow rate until it nears the t-stat setpoint and then will gradually reduce the flow as it achieves the setpoint. In essence, a variable speed circulator that recognizes coming out of a setback mode and can "boost" the flow-rate, in addition to a reset control that will boost the water temp as it comes out of setback. Should we just use a small wet-rotor impedance protected circulator as a variable speed circ to accomplish the same thing?

Any PID T-stats on the market that will work in conjunction with this soon to be released circulator? I think it would be an added benefit for comfort as well as efficiency. I know that Swampeast Mike loves his TRV setup and a mono-pumping zone is great for his particular setup, but new construction radiant floor heat (multiple zones) seems like it would be another step forward for the industry.

Any other thoughts on this?

Regards,

PR




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carol_3

I have no idea. Anyone else?

Aidan (UK)

PID T-stat

Do you mean using a variable speed pump to vary the flow rate for one zone? That is, as against having a constant speed circulator serving a manifold of TRVs with the TRVs varying the flow rates to the rooms they serve ?

I don't think there are any PID room stats. The P,I and D constants need to be tuned to suit the installation. You'd probably have to use a DDC or BMS controller with thermistor temperature sensors in each room. The PID control would be carried out in the controller by software control loops, which would typically give a 0-10V output control signal which would then control the pumps' speeds. I think the variable speed pumps can be configured to operate in response to an external control signal.

I've done something similar, but it used separate inverters, housed in a control panel, to control the pump speeds. The controls were done by a specialist contractor. It gets very complex, very quickly.

John McArthur_2

Aidan, sounds like you are describing a vsd pump control. I have installed vsd/vfd controls on large pump applications and see them used for well pumps. If pricing allowed I think it would work for radiant.

I like the idea of a vs pump for each zone. Maybe tekmar will develop a stat to directly interface with the pump.

Interesting topic though.

bob_50

Paul

I don't think you have to wait for Grundfos. Go to Taco's site and look at at 00-VV cartridge circulators. These are variable speed pumps available in all the 00 series sizes I believe. The speed is controled by any 0-10, 2-10, volt DC signal or 2-20ma. standard electronic control signals. They also have a switch to select linear or equal percentage output which would be very desireable for temperature control. I,m not up to speed on what M-H has for stats these days but there are tons of industrial temperature controllers with PID and the above output. Maybe a M-H R7380L1008, I'm not sure that control is PID. bob

Jed_2

Tekmar TN4

M/H just isn't cuttin it. Total feedback T'stats and integrated PID.

Jed