Heat Pump Recovery Thermostat: Temp Profile Not What I Expected

ColdMotiveNovember 26, 2012

My understanding is that modern heat pump thermostats anticipate changes in set point and act to ensure that the heat pump does the heating and not the auxiliary electrical coils. In addition I understood this meant that if one wanted the house at a certain temperature at a certain time one need not "second guess" the system by scheduling ramp up time, but instead let the thermostat figure it out.

The graph is a temperature profile shows that the heat pump doesn't start heating until the set point change at 5:30. And while it didn't trigger auxiliary heat it still didn't arrive at the desired temperature at 5:30.

Is this right

BTW: This is an American Standard system with AccuLink™ Platinum ZV Control

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I'm just a home owner, not a Pro.

My Carrier thermostat has a Setting to Enable/Disable the anticipatory temp ramp up.

I do not use this feature but rather choose to lock out the auxiliary heat source at or above 30 degrees and I lock out the heat pump below 30 degrees.

I note you expect the temp ramp-up to start some 3� hours before the end point. When I was "experimenting" with my Carrier equipment the ramp up started less than an hour before the end point.

    Bookmark   November 26, 2012 at 12:39PM
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Your thermostat may not have the recovery anticipation feature. See if you can find it in the installation manual. I have this feature but I turned it off on my Carrier thermostats.

Have you figured out why the temperature only reached 69 degrees and dropped back to 67? Are the labels on your graph correct?

An 8 degree set back is big for a heat pump. The recovery time will be long if the auxiliary back up is locked out. People who own heat pumps generally recommend set backs of 3-4 degrees.

    Bookmark   November 27, 2012 at 7:24AM
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I did 10F setbacks with my heat pump for some years when working two jobs. I was routinely out of the house for 14+ hours, 11 AM to 2 AM or later. Auxiliary locked-out to 25F. Recovery started 2 to 2.5 hours early and sometimes fell short of the target temp by a couple degrees at the target time, but didn't bother me in the least ... the system was running and blowing warm air so it felt perfectly comfortable.

I found that the Smart Recovery function took a few cycles to adapt to the profile it needed. It sometimes didn't ramp-up very far in advance (or not at all) if the drop-curve was mild and 4F to 6F instead of the full 10F.

    Bookmark   November 27, 2012 at 9:58AM
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It depends on the thermostat and it's setup. My White Rogers has 'anticipation' that adjusts depending on how well it hits the mark. But this can be set to what yours is doing in that it doesn't start until setpoint change time.

    Bookmark   November 28, 2012 at 3:50PM
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Regarding not reaching 70, I assume that the average temperature dropped in the house due to in=and-out activity that might also tend to distribute the mass of cold air from our less insulated rear porch. The next scheduled event is back down to 62 at 8:00 a.m.

I couldn't find the American Standard install manual online, but the same thermostat is available from Trane. I have excerpted what I think are the relevant controls to play with. I did look at these once, but was frankly too put off by all the double negatives such as, "disables the 10 minute inhibit" and "Heating Aggressive Recovery can only be enabled if Aggressive Recovery is disabled."

I'll be back home in two weeks and I can try to adjust these. Naturally, I will ask for advice here on anything I'm unsure of.

Aggressive Recovery:

This option disables the 10 minute inhibit anytime the thermostat sees more than a 2° change (such as moving from one program time frame to another). This applies to heating & cooling modes. Heating Aggressive Recovery: This option disables the 10 minute inhibit based on outdoor temperature in heating mode only. The value for outdoor temperature can be set from 0°��"70°. Heating Aggressive Recovery can only be enabled if Aggressive Recovery is disabled.There is a 10 minute “inhibit” period between first and second stage compressor as well as compressor heating & supplemental strip heat. This 10 minute inhibit period minimizes the cycling of higher capacity request due to drafts around the thermostat or marginal load conditions.

Cycle Rate

The cycle rate affects the cycle time of the system. With a 50% load value, a cycle rate of 3 will allow the system to run for 10 minutes and be off for 10 minutes; completing 3 cycles in one hour. A cycle rate of 5 would allow the system to cycle on and off at 6 minute intervals. The higher the cycle rate, the more often the system turns on and off. The actual amount of time the system will be “on” or “off” will be reflective in the load value of the home. Higher load value demands will increase system run time and decrease system off time. Lower load value demands will decrease system run time and increase system off time.Emergency HeatThe heat pump will be disabled and the furnace / heat strips are enabled any time the thermostat is set to Emergency Heat.


System lockouts will disable a certain function of the system under specific outdoor temperatures:Compressor Heating Lockout • ��" will lockout all compressor operation below a set outdoor temperature (from 5°��"70°). This value must be set lower than the auxiliary heat lockout. Auxiliary Heating Lockout • ��" will lock out auxiliary heat stages above a set outdoor temperature (from 40°��"70°). This value must be set higher than the compressor heating lockout. Defrost Heater Balance Point • for W1, W2 & W3 ��" will lock out specific auxiliary heat stages when above a set outdoor temperature. (W1 setpoint is from 40°��"55°, W2 & W3 setpoints are from 5°��"55°). This feature does not apply to dual fuel systems. Compressor Cooling First Stage Lockout • ��" will lock out the first stage compressor above a set outdoor temperature. (from 80°��"120°) Compressor Heating First Stage Lockout • ��" will lock out the first stage compressor below a set outdoor temperature. (from 0°��"50°) Furnace First Stage Heating Lockout • ��" will lock out first stage furnace operation below a set outdoor temperature. (from 15°��"50°) First stage lockouts are not available with zoning.

Setpoint Dead Band

This sets the temperature band between heating and cooling setpoints while in the auto mode.

Here is a link that might be useful: Trane Comfortlink II Installation Manual

    Bookmark   November 28, 2012 at 5:59PM
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SP Dead band: this just sets how close together you can have the Heating and Cooling setpoints. Usually this is 2*. For example, Heating to 70* and Cooling to 72*. Below 70* it switches to heat mode. Above 72* it switches to Cooling mode. In between it stays in whatever mode it was in.

Aggressive Recovery: Normally with a HP if you request more than a 2* temperature change the Tstat will automatically kick the system into high stage (for a 2-stage system). For heating this activates the auxiliary heat strips. Inhibiting 'aggressive' recovery tells the Tstat to wait 10 minutes before deciding to kick it into high gear.

Cycle Rate: This will set how many cycles per hour (more or less). Fewer cycles should give you longer run times but perhaps a larger temperature swing.

Lockouts: This is all dependent on whether you have an outdoor temperature sensor. If you do, then these lockouts let you do things like go to high stage immediately if the temp is low (for heat) or high (for cool) rather than wait 10 minutes, or go directly to Aux heating if below the effective heating point of the HP.

From looking at that manual, there is nothing there about 'anticipation'.

    Bookmark   November 29, 2012 at 4:45PM
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