Just a little concerned about run times for my DX heat pump.. it is 5 ton professional installed unit. It is new construction with good heat loss values. My concern is that the unit runs for 30 to 45 minutes at a time. is this normal or would this be considered out of the norm?
any thoughts would be great.

This is good.

A DX geo system should never exceed 90% run time. This would be 54 min. per hour. If it's running 30-40 minutes, it's still got extra capacity. You should notice that you're more comfortable and efficient with longer run times on forced air, too.

IMO, no geothermal heat pump should run for more than 90% of the time, so as not to "shock" the ground loop, or over-stress the loop.

So this is where the second stage plenum heat comes into play for extreme cold , -30 etc. to maintain the 90% or less run time.

Yep, if it gets that cold for very long, it'll basically protect the ground loop.

Where are you located?

Hey there, lurker chiming in.  My question would be how does the unit know when to kick in the electric coils to assist so that the compressor can stop?  Recently got over the local cold blast here in OKC ( temps in the low teens at one point) and my compressor ran 36 hours straight.  My system is a Climate Master GT-G with a CXM board.  Any thoughts?

The heat strip is controlled by the thermostat. What kind of tstat do you have?

Ok, this has me very confused. What is wrong with 100% duty cycle? Is there something unique with a DX system that doesn't allow 100% DC? It seems to me that for best overall efficiency that you want the system sized as close as possible to the projected maximum btu requirement during the coldest days.

Unless there is some required off cycle time unique to DX, I know of no technical reason to avoid long continuous run times. Some systems are designed for considerable heat strip operation on cold days, so the compressor operates continuously when load is such that strips are needed.

"Protecting the field" should be less of an issue for DX - no loop water to freeze?

During cooling season (seems like a distant memory right now) it is not uncommon for properly sized AC system to run for hours at a time on a worse-than-design day. There is no boost equivalent to heat strips for extreme cooling mode loads - we live with not quite making thermostat setpoints by a degree or so for 2-3 hours, but the increased dehumidification from continuous operation provides comfort even if thermostat setpoint is not quite attained.

I didn't exactly mean to hijack this thread.  I should state that I do not have a DX loop.  I just noticed the long run time in the title and was wondering also.  The Tstat i have can be found here:

http://www.commercial.carrier.com/commercial/hvac/product_technical_literature/1,3069,CLI1_DIV41_ETI4922_PRD775,00.html

Is there a nice way to say "inexpensive"?  I wouldn't mind replacing it.  It kinda looks like to me that it is a real cheap tstat to just get the house in a salable condition.  No frills.  Thanks so much for the interest.

Basic  is how I would describe what you have.  It does not give you any control over the back up heat.

I would get a tsat like this one.

With this  tstat  you set up your system to be a two stage heat pump with the back up being the second stage.  Then you can program the second stage to come on after  the first stage has been running  xx  minutes.  Where you choose the xx minutes.

Of course running 36 hours straight is not a problem unless your heat pump was not keeping up and  your house was getting colder.

On my computer you have to scroll way down the page to see the tstat. Just in case you go to that link and think the page is blank.

@ geodean There you go. That is exactly what I was thinking about as far as a tstat. I have noticed that the house is more comfortable with the long run time. It is just taking some getting used to it as I imagine the the electric meter spinning and smoking trying to keep up. :) I plan to start another thread for instrumentation and such for geo systems. Much thanks to you and also to the rest of you folks doing most of the replies on all these post. This forum has been fascinating for me. Thanks again. Joe

JoeinOKC ~

I completely understand your fear about the electric meter spinning 24/7, but just to ease some of your fears, I'll share what I've saved since October 22nd, 2008.

My system runs almost constantly like yours, but you can't make a direct comparison because my system is only 3 tons.  But this should give you some idea....

Based on my oil use rate per heating degree day from the past 4 years, I would have used over 230 gallons of oil since 10/22.  I used the cheapest price of oil on a weekly basis here in my area and assumed that I could purchase oil weekly at that cheapest rate (I understand that this is not possible).  With these VERY conservative assumptions, I still have saved almost $550 comparing what I have actually spent on electricity vs. what I estimated (conservatively) that I would have spent on oil.  (I've used almost 1,530 KWH on my geo system in the same amount of time.)

Now, this savings would have been much bigger with the price of fuel oil as it was when I purchased the geo system, but even with the fairly inexpensive price of fuel oil now (down to $2.75 this week), I am still ahead.

I'm not sure that it makes sense, but attached is a PDF of my spreadsheet that I keep.  I understand that it is not realistic that I would pay for oil on a daily basis at the lowest price, but this was the best way I felt I could make this calculation.

Good Post Ona

Ona, my electric consumption for December was more than 1600 KWH and cost me $315 ($39 gas and $277 Electric combined in one bill - with .11 per kwh  and I posted this on the other thread). So based on your post, that's still about normal then. I use oil in the past years and it went down to $2.44/ gallon in my area in New Jersey. Last year I spent about close to $2000 for the entire winter and we were still cold because we're trying to save money on the cost of oil ($3.54/gallon then)

We have a ClimateMaster thermostat with a 5 ton Tranquility 27 unit.

I am told there are 2 stages plus the auxilary electrical backup.

How do you know when the heat pump is running in second stage and also when the aux backup has kicked in?

Does the temperature have to be down so many degrees before the aux backup kicks in?

We are currently using 80 to 90 kilowatt hours a day due to our heat pump.

Does that sound reasonable for a 2,500 square foot bungalow 6 years old during a Canadian winter with temps between -15 and -20 

We have a ClimateMaster thermostat with a 5 ton Tranquility 27 unit.

I am told there are 2 stages plus the auxilary electrical backup.

How do you know when the heat pump is running in second stage and also when the aux backup has kicked in?

Does the temperature have to be down so many degrees before the aux backup kicks in?

We are currently using 80 to 90 kilowatt hours a day due to our heat pump.

Does that sound reasonable for a 2,500 square foot bungalow 6 years old during a Canadian winter with temps between -15 and -20 

What brand and model of thermostat do you have?

Ona,  I just visited your website.   way to go !!!

Thank You geodean.  I have been delinquent in uploading all my data, but that will come after the holidays.  I only wish I had planned on (or known about) a WEL system, that would have been a great tool!