How do you determine temp settings for an outdoor reset?

JPL

Hi -- I am new to the Wall and was hoping someone could point me at either a good website, or perhaps another thread, where I can get educated on how to choose setpoints for an outdoor reset control.



I recently had one installed that controls just one zone - the place where we spend most of our time. The guy that installed it didn't know a lot about it, and left it inoperable. After a few days with the manuals I sorted out some wiring issues (loose connections and miswiring), so it now appears to be mechanically doing what it's supposed to. I'm now down to programming it and don't know how to choose the setpoints.



The controller is a Honeywell T775R Series 2000 that basically just looks at the outdoor temp and the temp of the water right after a proportional mixing valve that mixes water direct from the boiler with return water from the radiator. The programming is simple. You just tell it what temp you want the mixed water at one outdoor temp, what temp you want the water at the another outdoor temp, and the controller assumes a straight line between the two for outdoor temps in between.



Could someone point me at a place where I can learn what the setpoints should be for my situation? I've done the heating loss calculation for the space, but I'm not sure what calculations I should do now to figure out where the setpoints should be.



Also, I've noticed that the water after the mixing valve never seems to get over about 140 deg, even though the boiler gage is reading about 180. This is with the modulating output at a full 100% for a period of time. The temperature sensor straps on the (copper) pipe and seems to be secure. Does this seem right? I would have thought it should be much closer to the 180, unless the mixing valve doesn't fully close one port so that you always get some of the return water being used. I don't know anything about this stuff, so I am really in the dark and guessing my way through it.



I'd really appreciate it if someone could point me in the right direction. I should have started at the Wall and got educated BEFORE I hired anyone to do something!!



Thanks very much.

Zman

Radiator

What type of radiator is the zone you are controlling?

If you compare the heat loss to the output of your radiator at a given temp, you will come up with your answer.

Carl

JPL

Cast iron baseboards

I have 30 feet of cast iron baseboard in that room. I believe the heat output is typically 600 BTUH/ft, but I'm not sure at what temp that is, and how the heat output changes with water temp. I'm sure I could find a table on that somewhere. Do I just determine the heat output required to maintain an interior temp (let's say 72 deg) at various outdoor temps, and then determine the water temps required? Are there any other considerations? Also, what do you think about the 140 deg reading at the mixing valve vs. the 180 at the boiler? The mixing valve is just a couple of feet from the boiler. Does it make sense that it's reading that low, or do I have a problem? Thanks for your help.

Paul48

Calibrated?

Is the temperature sensor calibrated, per  the instructions?

JPL

Sensor calibration

The manual describes how to calibrate the sensor by +/- 10 deg F (pretty simple), but I have no reference other than the boiler gage. I thought about buying an infrared thermometer at a hardware store, but they have an accuracy of only 4 deg, so I didn't know if that would be good enough. In any case, I couldn't adjust the reading by more the 10 deg.