Oklahoma New Install - ClimateMaster TE30-072 Delta T setting for Open Loop

Looking for info. We just replaced our TE27 (installed in 2009) yesterday with a new TE30. The old unit was replaced due to a refrigerant leak in the air coil, and several pinhole leaks developing in copper water lines to coax. The unit uses water from my home wells in a pump/dump (to the other well) open loop setup. Water quality is moderately corrosive with pH usually in the 6.5-6.8 range. Capacity of the well and GPM are not a limiting factor with a 2HP 45 GPM pump. We inherited this setup when we purchased the home a few years ago.

My question is should I consider having the installer change the default EWT / LWT delta T settings? The current settings are 10 deg rise in cooling, and 7 deg drop in heating. The unit manual has a table that shows "water temperature change through heat exchanger" for both closed loop and open loop systems. Beyond that, it doesn't go into many details about the advantages/disadvantages/reasons for the different settings. For closed loop, it states at 3 gpm/ton 9-12 rise for cooling and 4-8 drop for heating. Our current settings of 10 deg rise, and 7 deg drop are right in those ranges. On the other hand, for an open loop, it states 1.5 gpm/ton 18-24 rise for cooling and 10-17 drop for heating. The startup procedure on the prior pages also states to check that the delta T is in the normal range for operation with a similar chart showing the above numbers. I've read through the manual and it doesn't really explain much except 1.5 GPM/ton is the min for open loops, and that is scaling is a potential issue, more flow could be better, particularly with a cold water source. Scaling is not an issue with my water supply.

The unit appears to be functioning well so far. Some parameters measured yesterday during full load cooling were EWT-66, LWT-78 (12 deg rise), water pressure in 18 PSI, water pressure out 14.5 PSI (3.5 PSI drop). The charts show this is about 12-15 GPM flow through unit (which is 2.0 - 2.5 GPM/ton), or in the middle of the expected 1.5-3.0 gpm/ton. Air temp drop was around 30 deg, so was cooling well. The service tool showed the modulating valve was 100% open (which makes sense as it was attempting to attain the delta T of 10 degree rise in cooling.

What would be the advantage of setting the delta T in the range of 18-24 that the manual calls for? Is that the intent of that chart on pages 47-49 of the operating instructions? I understand less water would be going through the unit which could potentially lower pumping costs/water usage. For my situation, I'm also thinking that having less flow could lead to less velocities/turbulence in the water flow and could possibly result in less damage being caused by my corrosive water running through the unit. Maybe that reduced water flow would result in less chances this unit would experience the same copper pipe deterioration the old unit experienced over it's 14 year life? Is there any merit to this thought? Are there any other potential advantages? What about disadvantages? I'm sure there are some trade-offs that ought to be considered. The water flow through the modulating valve in an intermediate position will make a bit more "flow noise", but this is not an issue. I've read it could cause the valve to "hunt" to maintain the set delta T and it could result in constant hunting if incoming PSI varies.

For heating, in the winter as the water supply cools a bit, I'd have to watch out for ensuring LWT doesn't approach 40 deg due to lower flow with a larger delta T setting. Essentially, the delta T setting for heating will be limited/determined by water supply temp if the well cools off to the lower 50's. I don't think it gets that cold, but I'm not sure. We are in northern Oklahoma and the well pump is at 50', with static water level around 30', in case anyone is familiar with the groundwater temp fluctuations in the region.

Thanks for reading and for any advice regarding this question!

 

Sounds like you understand the issues.

I think the important points are:
1) higher flow results in slightly greater capacity and efficiency, but greater pumping costs, and
2) lower flow presents a potential freeze risk in winter due to the larger delta-t.

You could take some measurements of power consumption to assess the tradeoff, but I wouldn't expect the difference to be hugely significant.

You might want to look into whether a variable speed well pump would save you more.

 

Crickets eh? Update for anyone interested - I brought up my concerns again with the installer. They did eventually concur with adjusting the delta Ts. New delta T settings are cooling set to 16 degrees and heating set to 11 deg. There was some resistance to set both to the max values of 20 and 12, respectively, which the installer justified with some possible concerns of extra compressor wear in cooling, and LWT lockouts in heating depending on how cold the well gets. Said this is a good place to start, sounded good enough to me. Resultant measurements during cooling full load was a PSI drop of ~1.6 PSI which the charts show is about a 10-11 GPM flow. Part load cooling had a PSI drop of ~1.3 PSI equating to about a 9 GPM flow. Looks satisfactory to me. Don't be afraid to chime in if you've got any thoughts or experience to share!

 

Thanks! I think those are excellent points to ponder.