Virginia Upstairs WF Series 7 seems to spend a lot of time in stage 2 (full-load) cooling

Hi all,

I have a new construction 5000-ish sqft house in central VA with 2x Waterfurnace Series 7s (separate 4ton upstairs and downstairs units). I have noticed on the energy reports that the upstairs unit does not seem to spend much time in stage 1, or lower stage, cooling. It seems to jump up to mode "C-9" for a short period of time and then turn off when done. I rarely notice it ever in cooling modes less than 9 (my understanding is that modes 1-6 are reported as stage 1 or part-load and modes 7-12 are stage 2 or full-load). It doesn't seem to start at a low compressor speed and ramp up - it just starts on the high side. The fan speed however can be lower while this is happening. The downstairs unit seems to almost exclusively run in the lower stage (C-1 or C-2) and seems to be on for longer periods of time (seems to be working perfectly).

I spoke with my dealer an he switched the temperature differential settings that trigger the different stages from 0.5 degrees to 1 degree to try and force the 2nd floor unit to spend more time in the lower stage (I may not have the termininology correct here) but this doesn't seem to have made a big difference.

My understanding is that with the Series 7 the advantage is that it modulates over a range of compressor and fan speeds and should spend most of its time on and in the lower compressor/fan stages to allow for better energy efficiency, dehumidification, and comfort. It should increase to the higher power modes less frequently and in more extreme outdoor temperatures. We have a separate whole house dehumidifier so relative humidity has not been an issue.

Basically, I am worried that the upstairs unit seems to be short cycling rather than working as intended. Does this seem to be the case and, if so, is this ok? Can this be an issue with the settings or an equipment problem? I have attached two of the recent week-long readouts from the Aurora weblink, one for the downstairs unit showing that it almost always runs in stage 1 (part load), and another for the upstairs showing it spends much less time in stage 1 and more in stage 2 (full load). The temperatures here haven't been too hot lately so the overall energy usage is low (which should make it easier to run at the lower stage?).

Happy provide more info if needed.

Any help would be much appreciated,
Rich



First floor energy and part/full load usage




Second floor energy and part/full load usage

 

I am experiencing the same thing with my newly installed 7 Series. The first week or so it was deployed it didn't enter full cooling at all. After their final inspection by a 'senior tech' during which I saw full cooling and aux heat used the installer declared the system to be completed.

After that visit I'm seeing far more time in full cooling. Today, for instance, 100% of use is in full cooling mode (stage 9, like yours). Temperatures are still moderate here in New Jersey so total KWH for the day is nearly nothing but it seems strange.

I'm trying to wrap my head around the logic it's using to try to explain it but I'm not coming up with a lot. I know it needs to enter higher stages to ensure proper lubrication, and maybe on days which require nearly no cooling all the time running is spent in this stage? Overall it seems that a higher run time would be preferable for de-humidification purposes, if one was relying solely on the 7 Series for humidity control (which I am) is it to be expected that on days with essentially no cooling to do humidity will just be whatever it is?

To be fair this is currently an empty house with nobody going in or out, no real heat sources, etc.

 

You mention aux heat, hopefully it's not coming on during cooling...

 

No, just the day when the tech was there hooking the control up. I'm using a hydronic coil off of a Navien combi as backup heat, until that day the control was not in place for it. A tiny amount of aux heat was reported that day presumably during his testing, and none since. Tech was there on Friday. Every cooling day since has been entirely full cooling with no reported partial cooling or heat.

 

My unit was doing the same thing until I discovered it was due to the humidity setting that I had selected. Try raising the target humidity setting and see if it runs like your downstairs unit.

 

I can understand your confusion and the previous post about reviewing humidity setting is a good one; better yet, turn off the humidify function.

Just as FYI, the 7 series will always start up at C-6 for compressor oil circulation then ramp down in less than a minute. So you should expect that but your issue seems above and beyond that.