On Off heat pump cycles
Last Post 14 Aug 2010 09:50 AM by geodean. 13 Replies.
Printer Friendly
Sort:
PrevPrev NextNext
You are not authorized to post a reply.
Author Messages
nhgeo1User is Offline
New Member
New Member
Send Private Message
Posts:13

--
08 Aug 2010 02:03 AM
What is the best way to run the GSHP,.....a lot of short cycles or fewer long cycles?   I have been tracking my geo pump and it is averaging about 20-25 cycles a day.  The average run time is 10-20 minutes.  I do not have a programmable Thermostat.  I have adopted the "Set it & Forget It" school of thought on the tempiture setting.  I have both zones set at 76 ( 2 zone 2200sqft Energy Star, New construction house).

I am not woried about cost as I am for what is best for the unit.  I am very happy with the performance of the system so far.  My electrical cost average so far is $0.89 per day, and that includes the well pump for all domestic water usage.  ( open loop system)

The installer had been out recently and ran a performance test on the unit and the EER is 24, while the COP is 4.17

I have been thinking of getting a programmable thermostat, but it would only be for the benofit of the heat pump compressor if it is better to run longer cycles.  We are very pleased with how the system is performing and keeping the house at a constant temp.

engineerUser is Offline
Veteran Member
Veteran Member
Send Private Message
Posts:2749

--
08 Aug 2010 09:46 AM
Run the longest cycles you can consistent with remaining comfortable in the home. 20-25 cycles per day is not excessive. 10-20 minute run times may suggest unit is oversized for cooling if those run times occurred during times of record heat. That may be OK if you are in a heating-dominated climate.

Honeywell electronic thermostats have a setting to control # of cycles - CPH (Cycles Per Hour). Folks in high thermal mass houses may be comfortable with CPH of 2 or even 1; default setting is typically 3-4.
Curt Kinder <br><br>

The truth is incontrovertible. Malice may attack it, ignorance may deride it, but in the end, there it is - Winston Churchill <br><br><a href="http://www.greenersolutionsair.com">www.greenersolutionsair.com</a>
joe.amiUser is Offline
Veteran Member
Veteran Member
Send Private Message
Posts:4377
Avatar

--
08 Aug 2010 09:55 AM
If system seldom runs more than 20 minutes at loosley once per hour, it does sound a bit big for the job.
Joe
Joe Hardin
www.amicontracting.com
We Dig Comfort!
www.doityourselfgeothermal.com
Dig Your Own Comfort!
geomeUser is Offline
Advanced Member
Advanced Member
Send Private Message
Posts:987

--
08 Aug 2010 10:28 AM
Our installer started us off with 3 CPH. I found all the on/off cycles disturbing. After engineer explained that cycles may be bad on equipment, I started reducing the setting. We have a standard construction house and are still comfortable with 1 CPH (everyone may not be.) This holds +/-1f around our set point.

I have found that with our thermostat, 1 CPH actually runs 2 cycles per hour on our 2 stage equipment. When the thermostat is set for 1 stage equipment, it runs 1 cycle per hour.

What is the make and full model number of your current thermostat? It's possible that you may be able to access this setting in the installer setup without changing thermostats. I'd need to check the installation set up in the manual to be sure.
Homeowner with WF Envision NDV038 (packaged) & NDZ026 (split), one 3000' 4 pipe closed horizontal ground loop, Prestige thermostats, desuperheaters, 85 gal. Marathon.
nhgeo1User is Offline
New Member
New Member
Send Private Message
Posts:13

--
09 Aug 2010 07:51 AM
The cycles recorded were during the long stretch of heat we had.  The unit is a Hydron 2 stage 3 ton unit.  Listed below are some numbers from the Manual J.


                                            Sensible Gain      Latent Gain       Total Heat Gain       Total Heat Loss
 
Whole House 2,055.3 sq.ft.     19,648              4,929                24,577                      33,371


My concern regarding the cycles was for the long term health of the compressor and motor.  I may add a programmable Thermostat in the future to see if there are any energy savings.  The monitor system I am using allows me to watch in real time the amount of each circut in the house is using and keeps a historical base for it.

Mike
geomeUser is Offline
Advanced Member
Advanced Member
Send Private Message
Posts:987

--
09 Aug 2010 08:17 AM
Posted By nhgeo1 on 09 Aug 2010 07:51 AM
The monitor system I am using...
Which monitor system are you using?
Homeowner with WF Envision NDV038 (packaged) & NDZ026 (split), one 3000' 4 pipe closed horizontal ground loop, Prestige thermostats, desuperheaters, 85 gal. Marathon.
nhgeo1User is Offline
New Member
New Member
Send Private Message
Posts:13

--
09 Aug 2010 08:06 PM
I am using an Emonitor 24 by Powerhouse Dynamics.  It gives real time energy use, and I can track all of my circuts.  It has already saved me a bundle regarding the Hot water tank.  When the city inspected the plumbing, city code is the temp of the Hot Water tank is to be 140.   After 4-5 days I was wondering why a marathon tank was turning on so much.  I went and checked the temp, and the plumber forget to set the temp back down to 125 after the inspection. 

Without this monitor, I would have never known about it.  It is an expensive system, but I think it will pay for itself in a short amount of time.  I really wanted to be able to track the amount of electricity the geo unit uses and see how it compares to the design spec and projected operation cost.  This was the only system that I could find that would drill down to each individual circut.
joe.amiUser is Offline
Veteran Member
Veteran Member
Send Private Message
Posts:4377
Avatar

--
10 Aug 2010 09:22 AM
You appear to be in heating dominated climate. Heat pump is big for the job. A thermostat that lets you choose cph might be nice just so you can ensure 2nd stage cooling doesn't come on (unless you find you are not keeping up).
J
Joe Hardin
www.amicontracting.com
We Dig Comfort!
www.doityourselfgeothermal.com
Dig Your Own Comfort!
geomeUser is Offline
Advanced Member
Advanced Member
Send Private Message
Posts:987

--
10 Aug 2010 10:31 AM
Joe, do you mean setting stage one CPH to 2 or 3, and stage two CPH to 1 (for example)? This would be more automatic compared to what is listed below.

Another option may be to disable stage 2 at the thermostat and see if the system keeps up in cooling mode. Granted, manual intervention would be needed to switch the thermostat back to two stage operation if the system doesn't keep up.  If this is done, remember to re-enable stage two before winter.  Wouldn't want aux heat going on unnecessarily. 
Homeowner with WF Envision NDV038 (packaged) & NDZ026 (split), one 3000' 4 pipe closed horizontal ground loop, Prestige thermostats, desuperheaters, 85 gal. Marathon.
joe.amiUser is Offline
Veteran Member
Veteran Member
Send Private Message
Posts:4377
Avatar

--
11 Aug 2010 11:25 PM
I mean set stage 2 for 0 (y2 cooling). However now that you bring it up, I'm not sure it's an option on stats. I'm careful not to oversize systems so it hasn't come up for me. 
j
Joe Hardin
www.amicontracting.com
We Dig Comfort!
www.doityourselfgeothermal.com
Dig Your Own Comfort!
nhgeo1User is Offline
New Member
New Member
Send Private Message
Posts:13

--
12 Aug 2010 07:10 AM

When I gave the installer the plans and the projected Man J load for an energy audit co.  we based the 3 ton unit from that info. 

When the installer came out to measure the job and do the field measure for J Load, we discovered that the ceiling on the 2nd floor & the basement were not going to be spray foamed as I thought.  At that time the installer said the 3 ton unit would not be big enough for the heat loss.  I had the 2 mentioned areas spray foamed so the entire interior envelope was spray foam.  Our blower door test was projected to be about 1350 - 1400 and it came in at 725.  The house is a passive solar design that sits due South turned 2 degress to the east ( future solar PV system).  We have 10% glass on the South side using Marven Integrity casement windows.

Regarding a previous post, is this unit TOO big for the house??  We live in NH, so it is a heat dominated climate.  Of couse, we have had a lot of extened heat that we do not usually have. 

I tried an experiment the other week where I opened the all the windows & doors to the house early and got the temp down to 68 at 6:30 am.  Thermosat was set to 75.  The geo unit did not kick on unit 4:30 pm that afternoon.  The house seems to hold it temp pretty well I think, but I am basing that on our previous house.  Any thoughts?

joe.amiUser is Offline
Veteran Member
Veteran Member
Send Private Message
Posts:4377
Avatar

--
12 Aug 2010 08:37 AM
Curiously, my design software doesn't have new hampshire, but if we took Bangor ME for example a 3 ton would cover 99% of the heating and have a balance point of 0. This is using the 33,371 MBH you provided.
Not sure you are as cold as Bangor (it does get down there).
The problem is a 2 ton is small for the job in this scenario and 2.5 ton units aren't available in 2 stage.
j
Joe Hardin
www.amicontracting.com
We Dig Comfort!
www.doityourselfgeothermal.com
Dig Your Own Comfort!
geomeUser is Offline
Advanced Member
Advanced Member
Send Private Message
Posts:987

--
12 Aug 2010 03:01 PM
Posted By nhgeo1 on 09 Aug 2010 08:06 PM
I am using an Emonitor 24 by Powerhouse Dynamics.
Thanks for the info.  Neat looking unit.
Homeowner with WF Envision NDV038 (packaged) & NDZ026 (split), one 3000' 4 pipe closed horizontal ground loop, Prestige thermostats, desuperheaters, 85 gal. Marathon.
Palace GeothermalUser is Offline
Veteran Member
Veteran Member
Send Private Message
Posts:1609

--
14 Aug 2010 09:50 AM
..
Dewayne Dean

<br>www.PalaceGeothermal.com<br>Why settle for 90% when you can have 400%<br>We heat and cool with dirt!<br>visit- http://welserver.com/WEL0114/- to see my system
You are not authorized to post a reply.

Active Forums 4.1
Membership Membership: Latest New User Latest: hudson2000 New Today New Today: 0 New Yesterday New Yesterday: 2 User Count Overall: 34707
People Online People Online: Visitors Visitors: 122 Members Members: 0 Total Total: 122
Copyright 2011 by BuildCentral, Inc.   Terms Of Use  Privacy Statement