Infloor Zone thermostats

[markburtenshaw]

Just wondering how everyone out there with multiple zoned infloor applications deals with their thermostat setup. More specifically, if anyone uses the Heat Link thermostats and actuators.

The actuators are wax filled and can take upto 3 mins to even start opening, upto 6 mins to open fully. My understanding is this is to keep a large thermal mass moderately heated, i.e. don't try to throw lots of heat to it, just maintain. Everything works well, (house is super comfortable) we don't adjust the temperatures at night, but I do notice that the circ pump cycles on/off maybe a little more than I would like. Anyone use the wax filled actuators? or anyone mess around with the PID control of their thermostat?

 

[velvetfoot]

The system sounds quite nice. What's the downside of the circ pump cycling on and off? With multiple zones, doesn't the pump come whenever there is a call for heat from any one zone?

 

[markburtenshaw]

The system sounds quite nice. What's the downside of the circ pump cycling on and off? With multiple zones, doesn't the pump come whenever there is a call for heat from any one zone?

yes, pump will ultimately come on quite a bit with so many zones, but its almost short cycling. Right now the way the thermostat is setup there is no minimum on time when a call for heat happens, so it will turn on for 30 seconds then turn off, but as I mentioned earlier the actuator takes 3 minutes minimum to start flow, but mean while the circ pump is on and just going through the bypass. I'm playing around with the idea of increasing the minimum on time to satisfy the actuator opening up to get flow through the loop every-time there is a call....or maybe I just leave it and stop over thinking it!! Trying to make sure everything stays efficient from a thermal energy stand point and electricity stand point.

 

[TCaldwell]

Is there a deadband or differential setting on the thermostat to make it less sensitive? Pid with using a deadband around your temp setpoint might work as a thermostat, not to cycle as often. Do you have the ability to modulate your infloor mix temp, then you could control it through your plc's pid block.

 

[cpeltier]

PID combined with Outdoor Reset works very well. If you have well balanced zones from a temperature design standpoint then Outdoor Reset with simple on/off switch works.

 

[markburtenshaw]

Is there a deadband or differential setting on the thermostat to make it less sensitive? Pid with using a deadband around your temp setpoint might work as a thermostat, not to cycle as often. Do you have the ability to modulate your infloor mix temp, then you could control it through your plc's pid block.

Did a little more digging into the manual last night, and there are 2 modes it will operate in: Hysteresis (which would be On/Off) and Proportional Band (PWM). defaults to PWM, but noticed the minimum call for heat was set to 0 minutes, so this would cause it to cycle on and off multiple times untill the wax in the actuator is heated up enough to allow flow through. I bumped the max cycle time from 6mins to 15mins and then bumped the min. run time to 5mins. I just tried this on one zone to see how it reacts over the next few days. the first time it called for heat it did stay on until the actuators were open, so hopefully a set in the right direction. I will just have to see how close it follows the setpoint now, hoping it doesn't over shoot.

Yes, I do have a 4-way modulating mixing valve installed infront of the manifolds and it also has an outdoor reset, that part works very well.

 

[markburtenshaw]

PID combined with Outdoor Reset works very well. If you have well balanced zones from a temperature design standpoint then Outdoor Reset with simple on/off switch works.

When you say 'simple on/off switch' are you referring to the zone actuators? I'm still a little curious why they are slow acting wax actuators and not just on/off with physical adjustable flow control for each zone.

 

[cpeltier]

When you say 'simple on/off switch' are you referring to the zone actuators? I'm still a little curious why they are slow acting wax actuators and not just on/off with physical adjustable flow control for each zone.

Other posters on this forum have well setup ODR (Outdoor Reset) curves and have been able to eliminate the thermostat entirely. They just flick a switch on when the want to turn on the heat and the IFRH (In Floor Radiant Heat) circulator runs continuously. Most of us don't have our zones setup this well or can't due to our building characteristics and require PID zone thermostats.

I think your max cycle time needs to be adjusted for the mass of the radiant floor (I'm assuming it IFRH by the equipment). The higher the mass of the floor the longer the cycle time. On high mass radiant floors I have seen it as high as one hour. I believe the PI (Proportional Integral) function of the PWM thermostat will adjust the cycle time and the max setting is a limit. A PWM "pulse" of a few minutes is almost nothing on anything other then an extremely low mass floor hence the slow response of the wax. Another consideration is "zone synchronization". Some thermostats will coordinate with others in the house to synchronize the zone opening to minimize short cycling of the boiler and pumps. Tekmar controls definitely do this.