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Old 12-29-2008, 10:08 AM   #1
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HVAC Monitoring


I've lurked around here for a while and have found this forum to be a great resource. Thanks to the generosity of everyone here with their knowledge.

I've been trying to figure out some issues with my HVAC system that was installed in August. (More about that in another thread)

In the process of troubleshooting, I setup some monitoring to know how often the system was running, for how long, which stages of heat were coming on, temps, etc. I have my thermostat setup for 3 stages of heat. W1 is heat pump only, W2 is Stage1 of 5kw of heat coil, W3 is an additional 5kw. The only time the last 10kw comes on is during defrost or when the outdoor thermostat is below 15 degrees F. W2 wont come on until the heatpump has been active for at least 20 minutes and the temperature is still two degrees from the tstat setpoint.

I thought I'd share some of the charts here. The way you read the runtime, defrost and heat graphs...when it is solid, the state means true. So for the heat pump run-time, where it is orange, the system was operational.
Attached Thumbnails
HVAC Monitoring-hvac-runtime.png   HVAC Monitoring-hvac-temps-day.png   HVAC Monitoring-hvac-temps-minute.png   HVAC Monitoring-hvac-humidity.png   HVAC Monitoring-hvac-airflow.png  

HVAC Monitoring-defrost-week.png  

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Last edited by AndrewF; 12-29-2008 at 10:11 AM.
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Old 12-29-2008, 10:14 AM   #2
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HVAC Monitoring


Additional three charts. The last one includes readings from three rooms as well.
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HVAC Monitoring-w2-week.png   HVAC Monitoring-w3-week.png   HVAC Monitoring-room-temp.png  

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Old 12-30-2008, 12:09 AM   #3
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HVAC Monitoring


sorry but all i can say is holy s/h/i/t
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Old 12-30-2008, 06:00 AM   #4
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The heat pump in defrost graph, shows you have a problem.
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Old 12-30-2008, 08:41 AM   #5
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Quote:
Originally Posted by beenthere View Post
The heat pump in defrost graph, shows you have a problem.
I should also clarify, when it is below 15 out, the heat pump shuts off and the 10KW comes on....so to know whether it is really defrosting or not, one has to know the outside temperature...I think I need to wire up an additional relay that only triggers the monitoring system when the Defrost cycle is actually running.

The low for the 22nd and 23rd was down to 5. So there was a period of time where the outdoor tstat caused the 10kw to energize.

I did change the defrost timer cycle from being 30 to 60 minutes....that seemed to help.
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Old 12-30-2008, 02:21 PM   #6
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So your COP is less then 1.5, at outside temps of 5F, or less?
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Old 12-31-2008, 08:57 AM   #7
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Quote:
Originally Posted by beenthere View Post
So your COP is less then 1.5, at outside temps of 5F, or less?
My heat pump shuts off at 15 and switches to electric heat only.

According to manufacture specs. 17F cop is 2.30
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Old 12-31-2008, 11:32 AM   #8
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Quote:
Originally Posted by AndrewF View Post
My heat pump shuts off at 15 and switches to electric heat only.

According to manufacture specs. 17F cop is 2.30
5 KW of electric strip heat = 17,065 BTUs.
At 10 cents a KWH = $0.50 for 17,065 BTUs.

Same BTUs for a HP at a 2.3 COP = $0.28

Or exteneded a bit.
1,000,000 BTUs of electric strip heat, at 10 cents per KWH = $29.40
1,000,000 BTUs of heat from HP at COP 2.3 and 10 cents per KWH = $12.74

At 15, your heat pump is still above a 2 COP.

Running HP probably still cost less at 5 then just strip heat alone.
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Old 01-02-2009, 11:49 AM   #9
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Hmmh, I never did the math to that extent, which I certainly should have.

I have bypassed the outdoor t-stat for now. We rarely get below 10F around here anyways and I noticed when the temperature hovers around 15, there was a cycle where the HP would trigger the tstat falsely and it'd cycle HP on/off/on/off.

I am working on new monitoring charts for my system to calculate the total cost of usage since the last meter reading. These calculations will be based off of my run-time monitoring for each level of heat and combine them and known power readings using an AMP meter.
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Old 01-04-2009, 06:44 PM   #10
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Quote:
Originally Posted by beenthere View Post
The heat pump in defrost graph, shows you have a problem.
Tonight I added a few more probes to my monitoring system, including one on the outdoor condenser right next to the t-stat that triggers defrost.

When I opened up the outdoor unit, I found that the factory t-stat was lose from the coil, which could explain why some of the defrost cycles would take 10 minutes, which is when the on-board timer would terminate the cycle.
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HVAC Monitoring-hp-tstat.jpg  

Last edited by AndrewF; 01-04-2009 at 06:51 PM.
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Old 01-04-2009, 07:05 PM   #11
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Yep, that will cause problems.
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Old 01-04-2009, 07:23 PM   #12
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Quote:
Originally Posted by kennzz05 View Post
sorry but all i can say is holy s/h/i/t
Ditto.
People in emergency rooms get less graphs than this.
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Old 01-07-2009, 09:52 PM   #13
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I've been expanding my monitoring system and now calculate the cost per hour to run the HVAC system.

For example, I figured out that it cost me $10.16 to heat my house yesterday and the HP ran a total of 16 hours to do it.

For today, I have had 2 hrs of Defrost time....something isnt right on that one, I thought I fixed that when I re-adjusted the factory defrost t-stat. (see another thread for more about that)

I am not ready to share the URL publicly as it is a work in progress, but I have attached a snapshot.

At least now I'll have a before and after view from when I upsize all my supply/return duct work in the next couple of weeks and will be able to determine if it solved the lack of efficient problems I am having.
Attached Thumbnails
HVAC Monitoring-hvac-snapshot.jpg   HVAC Monitoring-hvac-defrost-cycle.png  
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Last edited by AndrewF; 01-07-2009 at 09:56 PM.
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Old 01-07-2009, 11:06 PM   #14
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Your air filter can effect how long a defrost cycle is.
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Old 01-07-2009, 11:44 PM   #15
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I dont have one right now....

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