Replies

1. 
   DaveRicheson | Aug 11, 2003 09:40pm | #1

   Short cycling will cause premature compressor failure. The refrigerant carries the oil through the compressor to lubricate it. When the unit short cycles, not enough oil is move, and the compressor will burn up in five to seven years, based on usage.

   Another problem with over sizing a unit and it short cycling is the lose of dehumidification. It may cool your house air but not run long enough to dehumidify the air. You will be cool and clammy.

   Loop size is based on heat transfer of the particular type of ground it is placed in. My FIL system is a 5 ton with 5 vertical loops of 165' each.

   Dave

1. 
   BillHartmann | Aug 11, 2003 10:47pm | #3

   How can oversizing the ground coils call short cycling?

1. 
   DaveRicheson | Aug 12, 2003 02:38am | #6

   To rapid heat exchange at the condenser will lower the head pressure and suction pressure. The compressor will shut down on the low suction limit. A throteling valve that operates off of the head pressure will probably work. Hope the installer is up on how to check superheat.

   Honeywell makes a pressure valve that will work for this application. Next question is how it will affect the condenser circulating pump. The only time I have used this set up was on water cooled condensers for  five ton Carrier units. One used our chilled water system for the condenser, and the other used domestic water. In neither case did we have to be concerned about causing to much head pressure for  a pump.

   Do you know how a single speed circulating pump would fare if you  choked down the supply say to 80%, or stacked up 10 to 20% more head pressure than its' rating?

   I don't have a clue, but am interested in how it might work.

   Dave

1. 
   BillHartmann | Aug 12, 2003 05:18am | #8

   "Do you know how a single speed circulating pump would fare if you choked down the supply say to 80%, or stacked up 10 to 20% more head pressure than its' rating?"

   A common centrifical pump can be throttled down without any problems. And typically the power demands go down. In fact you can run it deadheaded, the only problem is if you have a big pump all of the curning of the water in the dead head pump will cause it to heat.

   Actually this sound like a great application for a variable speed motor.

2. 
   CloudHidden | Aug 11, 2003 10:03pm | #2

   Go for a second or third opinion. I checked with the guy who did mine, and his off the top of the head guess is that for horizontal you'd need in the neighborhood of 800' of 1" pipe / ton. 5 parallel loops in a 200' trench 15' apart using about an acre of ground. He also said 1 1/4 pipe is not usually used in horizontal.

   Note that http://www.geothermalheatpump.com/how.htm mentions 700' to 1000'/ton for a slinky tube arrangement and suggests that's better than horizontal.

   My vertical installation in WNC is an 800' well (1700' of 1 1/4" tube) for a 4 ton pump.

1. 
   Tess | Aug 12, 2003 12:54am | #4

   Guys;we've heard of short cycling but feel that a valve plumbed into the feed or return line to throttle, if necessary,would avoid that problem.Water Furnace rep convinced us that slinky ground loop might be much to difficult to purge.Besides,our 11/4" poly is on its way;2000' of unbroken tubing.   Tess!

   Edited 8/11/2003 5:57:16 PM ET by tess

1. 
   CloudHidden | Aug 12, 2003 01:37am | #5

   After you have it running, it should be interesting to see the performance. Based on temp differentials and flows, they should be able to tell the btu's it's producing. I hope you come back and tell us how it performs.

1. 
   Tess | Aug 12, 2003 04:48am | #7

   We hope to be with this heating system by October.Will let all know of performance.From several posts we are somewhat concerned about oversizing the loop and may make adjustments.Thanks for your imputs.Tess