Honeywell RTH7500D Thermostat Heat Pump Cycle Rate

Reply

  #1  
Old 12-28-15, 06:26 PM
4
Member
Thread Starter
Join Date: Aug 2012
Posts: 10
Received 0 Votes on 0 Posts
Honeywell RTH7500D Thermostat Heat Pump Cycle Rate

I have a heat pump in the attic (with electric coil backup), which is very cold in the winter. The Honeywell RTH7500D cycles the heat pump for about 5-10 minutes every so often. This is barely enough time for the system to get a decent temperature to warm the ducts, etc, and finally blow warm air. The problem is, I think since I set it to control a heat pump, it takes away option 240, which is Heating Cycle Rate, and I only have control over 270, which is Aux Heating Cycle Rate. I would like it to run less often for a longer time so everything in the system doesn't cool down just in time to start again...any suggestions?

Thanks
 
  #2  
Old 12-28-15, 06:46 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 61,483
Received 1,421 Votes on 1,314 Posts
It looks like 240 is not a heat pump function. Not quite sure what the 270 does.

Name:  honey.jpg
Views: 2063
Size:  30.1 KB
 
  #3  
Old 12-28-15, 10:23 PM
Houston204's Avatar
Forum Topic Moderator
Join Date: Oct 2009
Location: Texas
Posts: 7,425
Received 17 Votes on 14 Posts
Set function 270 to 3. This controls the heat strip cycles per hour.
This will give you longer cycles and increase comfort.
 
  #4  
Old 12-29-15, 07:50 AM
B
Member
Join Date: Mar 2015
Location: Canada
Posts: 186
Received 0 Votes on 0 Posts
I have my cph on my heat pump set all the way down to 1.... back up heat at 3. Heat pumps should run long and continuous. (higher end thermostats will allow you to customize your cph)

The cycling is SUPPOSED to add comfort in keeping the house at a more even temperature, but with a heat pump (and maybe it's just me) but I notice absolutely no difference in comfort level between 1 and 3.
This is probably due to the fact that it takes a heat pump a bit of time to stabilize and actually start producing heat so each time it has to cycle it's not really producing any real heat for up 5 minutes at the beginning of each cycle. Heat strips produce heat almost immediately so they DO add a bit of comfort with a higher cycle rate.
 
  #5  
Old 12-29-15, 08:03 AM
4
Member
Thread Starter
Join Date: Aug 2012
Posts: 10
Received 0 Votes on 0 Posts
This is exactly what's happening. The thermostat is controlling the temperature so close that it only needs a fraction of a degree to satisfy it and turn it off. The backup coils never even turn on for the short time it's on. Does setting 270 somehow control the heat pump as well as the aux heat? I have the aux set at the Honeywell recommended 9, but the aux heat definitely does not come on 9 times per hour, I don't think it even comes on once per hour unless it's trying to raise more than 1 degree, or it's very cold outside.
 
  #6  
Old 12-29-15, 08:51 AM
B
Member
Join Date: Mar 2015
Location: Canada
Posts: 186
Received 0 Votes on 0 Posts
The thermostat is controlling the temperature so close that it only needs a fraction of a degree to satisfy it and turn it off.
Well, it's not really doing it on temperature. It's doing it through straight mathematics. It's dividing your heating requirement up over 3 cycles (with a setting of 3)

270 only controls your back up heat.

The manual states that you should be setting 0170 to 7 (Heat pump WITH back up heat).

Unfortunately I don't believe that stat has the ability to customize your cph values for a given heating system. If you wish for a lower cph value on your heat pump then you will have to purchase a higher quality stat. Honeywell is a good company but they go crazy over the idea of 'comfort' and their standard cph settings are always higher than I like. If I get Honeywell I always make sure it has a customizable cph ability.
 
  #7  
Old 12-29-15, 06:35 PM
4
Member
Thread Starter
Join Date: Aug 2012
Posts: 10
Received 0 Votes on 0 Posts
Thanks for the response. This is helpful. Do you know of a thermostat that does allow control over cph for the primary source? I ask because I would've assumed that the RTH7500 does (setting 240), except it does not allow it when using a heat pump (they don't seem to tell you this anywhere)....I wouldn't want to buy another model/brand only to find that it has the same restriction
 
  #8  
Old 12-29-15, 09:06 PM
B
Member
Join Date: Mar 2015
Location: Canada
Posts: 186
Received 0 Votes on 0 Posts
I have a high end stat (Honeywell Prestige 2 IAQ) and it has completely customizable cph... but I'm not sure you want to spend that much money.

You can go here and download the manuals and find one if you wish:

https://www.forwardthinking.honeywel..._products.html
 
  #9  
Old 12-30-15, 06:15 AM
4
Member
Thread Starter
Join Date: Aug 2012
Posts: 10
Received 0 Votes on 0 Posts
Thanks!! Those are pretty expensive...at least I know an option if this gets too annoying.
 
  #10  
Old 12-30-15, 11:19 AM
D
Member
Join Date: Dec 2012
Location: United States
Posts: 254
Received 1 Vote on 1 Post
I've been very happy ( for 5 years now) with a Robertshaw RS4320, 3heat / 2 cool , which offers control settings as times and temperature differentials rather than cph . Maybe it's because it suits my household and the idiosyncrasies of my heat pump (York) - I know that Honeywell seems to be the preferred thermostat here -- but since you ask for something of modest price (it's ~$60), you might want to check it out, especially if you want more direct control than cph offers.
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: