Just replaced my 18 Year old WF with a new TE-30 using open loop. Question about Delta T for this setup. I always thought Delta T was computed using EWT-LWT. Is this correct or is it LT1-LT2? The reason I ask is that in the manual it states that water temperature change should be 18-24 for cooling and 10-17 for heating. This particular unit has an automatic modulating valve installed and it can be configured for Delta T or a fixed percentage of flow. When attempting to set the Delta T for each mode it allows a maximum of 20 degrees for cooling and 12 for heating. It just seems to me that it should allow the maximum of 24 for cooling and 17 for heating if that is the acceptable range. When the unit was installed it was set for 7 heating and 12 cooling. I have a minimum LWT of 70 degrees set. So, when operating using the Delta T of 20 the modulating valve overshoots the the temp ranges and then knee jerks the other direction over shooting again. Example using a Delta T of 20 in cooling with a 77 degrees room temp and 74 setting: Starting: EWT 54 LWT 66 Valve 94% 1 minute later: EWT 54 LWT 71 Valve 71% 1 Minute later: EWT 54 LWT 78 Valve 53% This process then reverses with the valve opening back up to the 90% range and LWT falling back to 66-67. When the Delta T settings were set to 12 for cooling the modulating valve appeared to be more stable staying in a tighter range.
There are many different operating conditions that effect DeltaT. Published acceptable ranges run to either end of the operating envelope of the machine. In most cases it is not prudent to run them to the edge. I suppose this is why ClimateMaster has limited the programmable DeltaT in VFlow applications. There can be many different causes for your modulating valve to hunt around. One of them is too high or varying supply pressures. See the Trouble Shooting Guide Page 47 available here- http://www.climatemaster.com/geothermal-dealer/te/
Thank you for the reply. I am running a variable speed well pump set to 40 PSI and have a 30 PSI reducing valve installed on the TE30. I checked jumper A0-2 to make sure it was set for 0-10V instead of PWM. Also made sure all dip switches were set properly. The unit itself is doing a good job cooling. Yesterday, the air leaving the unit was a fairly consistent 45F with return air 75F. I just don't understand why the modulating valve is hunting on such a wide range. All temp sensors appear to be functioning and display through the communicating thermostat. It appears to me that the unit does not let the current valve position stabilize long enough before making adjustments and then adjusts too far. Since my water stays pretty much 54F constantly I'm thinking a better solution would be to set the modulating valve to a fixed amount that allows for roughly 6.0 GPM (open loop) for cooling and roughly 7.5 GPM for heating. According to the manual that should yield roughly a 20F delta T for cooling and 10 for heating. I must provide a little more water in the winter due to being too close to a LT1 lockout scenario at 6.0 GPM in heating mode.
It sounds like you are doing everything right. On an open loop system you also should check that your discharge system pressure is not climbing or fluctuating excessively. Perhaps you can ask your ClimateMaster dealer or distributor how the modulating valve is controlled and determine if there is an issue with the control. That would work but you would be flowing to much during 1st stage operation.
The interface gives you the ability to set valve % opening for both stages of heating and cooling. It just seems that may a better solution if the valve does not stabilize. Like I said, it is performing well from a comfort standpoint, but I think I am wasting a lot energy pumping water I should not be pumping. If it is acceptable to interpolate the temperature performance charts bewtween 50 and 60F (they are listed in 10F incredments) I should be using roughly 20F Delta T at 6.0 GPM with a 54F EWT. In the winter my EWT drops down to 52-53F and figuring that I don't want to be less than 40-41F LWT in heating I should be able to flow roughly 7.5 GPM and achieve desired results.
I didn't know you could run different %'s at different stages. Thanks for the correction. It sounds like you have a good plan based on your conditions.
Thanks. I'm going to have the installer look it over again to make sure all pressures and temps are in spec before proceeding, but from what I can gather with a constant EWT and the ability to stabilize the incoming pressure at 30 PSI I should be able to manually dial in the flow rates to achieve maximum efficiency. The communicating thermostat and the ability to measure EWT/LWT/LT1/LT2 on it was the main reason I bought the CM. It is nice to see at a glance what the condition of the unit is.
Decided to try a fixed setting for the modulating valve targeting a 75 LWT for the water which is a 20F Delta T. I set the first stage at 62% and second at 72%. This resulted in very stable operation and results very close to what I was looking for. I’m going to verify that the water flow is around 6 GPM for this 4 ton system at this setting. Since I have a constant EWT I don’t see any reason to use the automatic modulating valve when I can get stable results from fixed. I love the feedback the thermostat gives and the ability to fine tune the water flow through it.
