New geo install may be short-cycling
Last Post 17 Aug 2014 09:15 AM by G.O. Joe. 25 Replies.
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EvilTwinUser is Offline
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08 Aug 2014 11:01 AM
Hello. I am new to the forum, having been reading posts for a while as we have been progressing through a new Geothermal installation. We are nearing the end of this process and I want to ask some questions to gain some additional perspective on what my installer is telling me and what I am seeing in the data collection coming from the monitoring system. About the system: The house is a 4400 SF colonial we purchase in February of this year and we had two installers perform manual J calcs at the start of this project. Both came up with just over 60000 BTU and sized for 5 ton. We were going from a 20 year old pair of oil furnaces along with two 4-ton AC units. The ducting was zoned with one system servicing each zone. The loop field is a horizontal slinky, all buried at 6 feet. The unit that was installed is a 5-ton Climatemaster Tranquility 30 Digital with a desuperheater along with a zoning control panel and dampers installed to control each zone. The returns from each zone are tied together where they enter the return on the pump. So my main concern is this...As I look at the data I am getting from the monitoring system and I listen t/watch the unit function, it appears to me to be short-cycling, something our old AC system did constantly at the beginning of the season. For cooling, the systm has been coming on every 15 minutes like clockwork and then running for approx 5 minutes then shutting off. There are two thermostats, one in each zone (upstairs/downstairs). The stats are set to only allow four cycles per hour. If the system would be allowed to call for cooling more often, I believe it would. I have seen several times where the stat would call for cooling, but because of the cycle limit the stat would prevent the system from coming on until the 15 minutes had passed. It will do this all day long, from about 10AM until temps go down overnight, say 2-3AM. My installer says that this is normal. Temps have been mild here, mostly low to mid 80's. The system has been running for 3 weeks. I will admit that the house is quite comfortable (something the installer keeps focusing on) yet I can't believe that the cycling like this is normal. I am looking for some feedback. I can provide more details if needed. I want to be happy with this system and have it be as efficient as possible but I'm struggling with this issue and want some peace of mind before I am done paying the installer and they move on. Thanks.
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08 Aug 2014 12:29 PM
Posted By EvilTwin on 08 Aug 2014 11:01 AM
Hello. I am new to the forum, having been reading posts for a while as we have been progressing through a new Geothermal installation. We are nearing the end of this process and I want to ask some questions to gain some additional perspective on what my installer is telling me and what I am seeing in the data collection coming from the monitoring system. About the system: The house is a 4400 SF colonial we purchase in February of this year and we had two installers perform manual J calcs at the start of this project. Both came up with just over 60000 BTU and sized for 5 ton. We were going from a 20 year old pair of oil furnaces along with two 4-ton AC units. The ducting was zoned with one system servicing each zone. The loop field is a horizontal slinky, all buried at 6 feet. The unit that was installed is a 5-ton Climatemaster Tranquility 30 Digital with a desuperheater along with a zoning control panel and dampers installed to control each zone. The returns from each zone are tied together where they enter the return on the pump. So my main concern is this...As I look at the data I am getting from the monitoring system and I listen t/watch the unit function, it appears to me to be short-cycling, something our old AC system did constantly at the beginning of the season. For cooling, the systm has been coming on every 15 minutes like clockwork and then running for approx 5 minutes then shutting off. There are two thermostats, one in each zone (upstairs/downstairs). The stats are set to only allow four cycles per hour. If the system would be allowed to call for cooling more often, I believe it would. I have seen several times where the stat would call for cooling, but because of the cycle limit the stat would prevent the system from coming on until the 15 minutes had passed. It will do this all day long, from about 10AM until temps go down overnight, say 2-3AM. My installer says that this is normal. Temps have been mild here, mostly low to mid 80's. The system has been running for 3 weeks. I will admit that the house is quite comfortable (something the installer keeps focusing on) yet I can't believe that the cycling like this is normal. I am looking for some feedback. I can provide more details if needed. I want to be happy with this system and have it be as efficient as possible but I'm struggling with this issue and want some peace of mind before I am done paying the installer and they move on. Thanks.

Fewer CPH (cycles per hour) means wider temperature swings, BUT longer run times.  Longer run times increase overall efficiency, reduce wear and tear on equipment due to fewer start/stop cycles, improve overall desuperheater efficiency and dehumidification in cooling mode.  The longer your unit runs at steady state (instead of excessively cycling on and off), the better (subject to comfort.)

You may want to try 2 CPH  and observe (and see if you like) the results and adjust if desired.  If your thermostats are tied together with a zoning unit, you will need to find out how to adjust the CPH correctly since CPH may be controlled from the zoning unit.  If the thermostats are not tied together, the CPH should be adjustable from each thermostat.
Homeowner with WF Envision NDV038 (packaged) & NDZ026 (split), one 3000' 4 pipe closed horizontal ground loop, Prestige thermostats, desuperheaters, 85 gal. Marathon.
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08 Aug 2014 12:53 PM
Unfortunately, the thermostats only allow for 4 or 6 CPH. I cannot do 2 CPH. The thermostats are Climatemaster units. Sadly, they are not the digital communicating thermostats, either, as those are not compatible with the zoning board. The documentation I have or the zone board does not indicate it has anything to do with the cycling limits. It looks like it is all coming from the thermostats. What I have debated doing, and asked the installer to try, is to take the zoning out of the equation and simply hook the main floor thermostat directly to the unit. My thinking being that if the system is properly sized for 5 ton, the zoning is essentially making a 5 ton system cool two 2.5 ton zones, one at a time, thus the cycling. Is this a reasonable theory and approach for troubleshooting?
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08 Aug 2014 01:28 PM
I'm sure the Pro's here can help you with the additional info you provided. We have independent thermostats controlling two separate units.
Homeowner with WF Envision NDV038 (packaged) & NDZ026 (split), one 3000' 4 pipe closed horizontal ground loop, Prestige thermostats, desuperheaters, 85 gal. Marathon.
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09 Aug 2014 07:47 AM
Zoning a 5 ton heat pump can be tricky for sure.

What model zoning board do you have?
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09 Aug 2014 08:13 AM
Posted By heatoftheearth on 09 Aug 2014 07:47 AM
Zoning a 5 ton heat pump can be tricky for sure.

What model zoning board do you have?


Thanks for resopnding. The zoning board is a Jackson Systems Z-300-HPS http://www.jacksonsystems.com/products/jackson-systems-zone-control-panel-2.html
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09 Aug 2014 10:21 AM
Is it the same zone that is calling for cooling and causing the short cycling?

You might try keeping the fan mode switched to on rather than auto.

You are correct to be concerned with short cycling.

You should be able to program a wider differential on the climatemaster stat. do you know where it is set now?

If comfort doesn't suffer, you might try eliminating the zoning, the unit will certainly be happier.
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09 Aug 2014 10:43 AM
You should verify that when a zone is off, the damper doesn't close completely. This is an intermediate step towards no zoning (which is worth trying but may not maintain a comfortable balance as conditions change).
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11 Aug 2014 09:53 AM
Where do you live? If 60,000 BTU's was your heat loss, then your cooling load is likely much smaller and the unit over sized.
Because you limited the number of cycles, is your house temp more than one degree from the set point when unit comes back on? You may be jumping right in to second stage.
Joe Hardin
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11 Aug 2014 10:51 AM
I'm in the suburban Philadelphia area. The number of cycles is being limited by the thermostats. By default, they are set to 4 cycles per hour max. The only other choice is 6 CPH. The house temp never gets more than one degree from the set point before it calls for cooling again. It was asked earlier if the second zone calls for cooling before the 15 minute lockout is up on the first zone. I want to say yes but I am not 100% certain on that. I need to observe some more. I also don't know if the Climatemaster thermostats that are controlling the cycling lockout together somehow or if that control is happening at the heat pump itself. I was told that the dampers that were put in for the zoning were Barometric Zone Dampers. My understanding is that even when a zone is not calling for cooling, it will still receive some cooling if the other zone is calling. Not sure if this is impacting the system or not.

The installer is generally telling me that the weather has been mild and therefore the system is not having to work very hard to cool the house. I can understand that but it still shouldn't short-cycle. I don't want to be replacing my unit sooner than necessary. I expect to get a lot of life out of it.
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11 Aug 2014 11:40 AM
it still shouldn't short-cycle


I am going to take a look at this from a nontechnical, logical view.

1-ClimateMaster knows their product better than anyone else.
2-ClimateMaster has programmed their thermostat with a 4 cycle/hour Min (default option).

My conclusion is 4 cycles/hour is NOT short cycling according to ClimateMaster (unless you believe they are controlling it this way so it will blow up immediately after the warranty is over).
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11 Aug 2014 11:57 AM
Posted By G.O. Joe on 11 Aug 2014 11:40 AM
it still shouldn't short-cycle


I am going to take a look at this from a nontechnical, logical view.

1-ClimateMaster knows their product better than anyone else.
2-ClimateMaster has programmed their thermostat with a 4 cycle/hour Min (default option).

My conclusion is 4 cycles/hour is NOT short cycling according to ClimateMaster (unless you believe they are controlling it this way so it will blow up immediately after the warranty is over).


I get what you are saying here and logically it makes sense. But keep in mind that there is a zoning system in the middle of all this that the Climatemaster components are ignorant of. The zoning board takes input calls from two separate thermostats and based on those inputs (a) turns on the system and (b) opens/closes appropriate dampers. So logically, I have a 5 ton system feeding a 2.5 ton space at any one time unless both zones are calling for cooling at the same time. Also, the 4CPH is a Max, not a MIN. Now, if someone from climatemaster tells me that 4 or 6 CPH is well within their expected performance parameters, I guess I'll be fine with that. But anything I ever read or was told about hvac systems says that a system that comes on for 5 minutes, turns off for 10 then continues to do that endlessly is short-cycling and that is bad.
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11 Aug 2014 12:36 PM
was that 60,000 the heating load? if so then you are oversized. Make sure only first stage is activated for cooling during these cycles, but there is little you can do with a large unit, and low demands due to outdoor temperature.

Sometimes you have shorter cycles because there isn't a lot of demand. You can't make it run longer unless you can change the "droop" (spread between set point and activation of unit) on your thermostats. Don't worry, winter is coming soon and you'll have plenty of long cycles.
Joe Hardin
www.amicontracting.com
We Dig Comfort!
www.doityourselfgeothermal.com
Dig Your Own Comfort!
G.O. JoeUser is Offline
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11 Aug 2014 12:52 PM

I am going to take a look at this from a nontechnical, logical view.

1-ClimateMaster knows their product better than anyone else.
2-ClimateMaster has programmed their thermostat with a 4 cycle/hour Min (default option).

My conclusion is 4 cycles/hour is NOT short cycling according to ClimateMaster (unless you believe they are controlling it this way so it will blow up immediately after the warranty is over).




Add in
3-The ClimateMaster DXM2 Control has a 5 Minute short cycle timer programmed in.

Same Conclusion - you are NOT short cycling
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11 Aug 2014 05:47 PM
A barometric damper may have been put in to limit the supply duct pressure when only one zone is in use, but it still needs thermostatically controlled dampers to control which zones get cooling. Tying the returns together (presumably without dampers) means that you are creating a negative pressure in the not-in-use zone. That's a bad idea that causes air, moisture and pollutants to be pulled through your walls.

I'd try it without zoning and use fixed register adjustments. You will get longer run times and fewer pressure balance problems.
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13 Aug 2014 06:03 PM
But anything I ever read or was told about hvac systems says that a system that comes on for 5 minutes, turns off for 10 then continues to do that endlessly is short-cycling and that is bad.


Emerson/Copeland says 10 starts per hour max.
Danfoss says 12 starts per hour max.

Conclusion in the study (link below) 3 to 4 starts per hour max should be optimum for efficiency.

Technical View - Effects of cycling on domestic GSHPs Link
https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/198854/mimer_report_on_modelling_cycling_of_heat_pumps.pdf
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13 Aug 2014 09:58 PM
As the study says "Steps should be taken by the designer/installer, to ensure that under all load side operating conditions, the heat pump will run for a minimum time of the order of ~10 minutes." The OP is at 5 min, which is a short cycle from an efficiency standpoint.
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13 Aug 2014 11:46 PM
I'll let you all be the judge. Here's the web-enabled data collection. Have a look.

http://myewise.net/site.php?id=3213
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14 Aug 2014 08:51 AM
Again it's big for the job and the weather is marginal. See if you can adjust droop.
Joe Hardin
www.amicontracting.com
We Dig Comfort!
www.doityourselfgeothermal.com
Dig Your Own Comfort!
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14 Aug 2014 02:53 PM
Posted By joe.ami on 14 Aug 2014 08:51 AM
Again it's big for the job and the weather is marginal. See if you can adjust droop.


To do this, I would need to set the "Temperature Algorithm" from its current default of Proportional Integral to Differential. The differential settings are currently 1 degree between each stage. Setpoint is currently 76, so stage1 at 77, stage 2 at 78 (5 minute minimum at stage 1). Since this is likely just going to be a trial and error, would you recommend starting with the first stage at 2 degree differential? Should I set both thermostats or just one? Thanks for all the help thus far.
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