[KISS]

There is no FF kit from Honeywell.
The t-stat suggested does allow -12C for a lockout temp.

So, only real problem I can possibly forsee relates to the hysteresis of your -12C lockout. If there is none, then the compressor MIGHT turn on and off suddenly under high head pressure and may pop the heat pump fuse UNLESS the HP has it's own built in anti-short cycle relay.

I've seen fuse holders blow up because there was no anti-short cycle. The VP does have it built in as an option, but it won't know if you turned the compressor off externally.

That kind of relay prevents restarts for a given amount of time after a power fail or after the contact switched off.

[LouisB]

There is no FF kit from Honeywell.
The t-stat suggested does allow -12C for a lockout temp.]

If I understand the HW instruction sheets, I would be required to install their External Sensor for this. In my case the Utility provides this component. It is a switch and is quite accurate.

[So, only real problem I can possibly forsee relates to the hysteresis of your -12C lockout. If there is none, then the compressor MIGHT turn on and off suddenly under high head pressure and may pop the heat pump fuse UNLESS the HP has it's own built in anti-short cycle relay.]

The problem is not with the -12C contact, but with high head pressure developing when the gas is being overheated while the compressor is active, not when it is locked out. The HP becomes available after the FF relay is deactivated by the thermostat, and same thermostat completes any remaining preset delay between HP cycles. Any head pressure would have had time to deplete while the FF heat source was active.

[I've seen fuse holders blow up because there was no anti-short cycle. The VP does have it built in as an option, but it won't know if you turned the compressor off externally.]

I can see this being a problem area when the HW solution is to work the HP between sensor provided lockout set points..and knowing the sensor is hysteresis prone.

[That kind of relay prevents restarts for a given amount of time after a power fail or after the contact switched off.]

This would be a time delay relay having a variable time to lapse before the contacts are made to move. This would for certain circumvent the compressor being reenergized too soon before the high head pressure depletes itself throughout the refrigerant circuit.

Again, thank you for your valuable assistance.

[KISS]

It's not a time delay relay in the traditional sense. See http://www.ssac.com/catalog/TA001A01.pdf
for an appropriate timer. They work well. They have other models as well.

This function seems to be assigned to the t-stat now.

There are some applications notes ion their website as well.

One one has lots of AC compressors and the building has a power failure, all the AC's try to start at the same time. There are models that randomize that delay.

The site takes a little used to to navigate. SSACis a division of Allen Bradley.

About $22 from SSAC TA24, 24 VAC Timer with time delay

Thinking out loud: What has to be done, if anything to the fossil fuel control? What happens if there is chatter?

KISS

[LouisB]

It's not a time delay relay in the traditional sense. See http://www.ssac.com/catalog/TA001A01.pdf
for an appropriate timer. They work well. They have other models as well.

This function seems to be assigned to the t-stat now.

There are some applications notes ion their website as well.

One one has lots of AC compressors and the building has a power failure, all the AC's try to start at the same time. There are models that randomize that delay.

The site takes a little used to to navigate. SSACis a division of Allen Bradley.

About $22 from SSAC TA24, 24 VAC Timer with time delay

Thinking out loud: What has to be done, if anything to the fossil fuel control? What happens if there is chatter?

KISS

Thanks for the suggested relay.. will keep the lit in file in case, but as you suggest the thermostat does have a adjustable time delay (0-5 minutes) before compressor restart, called "Minimum compressor off time". At any rate any FF on time will likely exceed 10 minutes including plenum cool down.
FF relay chatter? Don't know how this could occur, other than the thermostat chopping the 24V feed. Unless there is possible conflict at the thermostat when it calls for compressor "on" and the "Y" feeder is open, and this while it also calls for auxiliary heat? Now that would be a strange design flaw, and contrary to any optional use with a FF Kit.
LouisB

[KISS]

I'm suggesting that if the -12C lockout is in control, it could cause chatter.

The tstat isn't going to know that the compressor kicked off when the thermostat thinks it's on when the -12C lockout did it. I's suspect it should know if power Rh was removed.

[LouisB]

I'm suggesting that if the -12C lockout is in control, it could cause chatter.

The tstat isn't going to know that the compressor kicked off when the thermostat thinks it's on when the -12C lockout did it. I's suspect it should know if power Rh was removed.

Let me elaborate a bit on the circuit. The 24V ("Y") feeding the compressor first meets up with two sets of contacts at the interposing relay associated with the -12C switch. One set is NC and thus continues the feed to the compressor when HP is called for heat. Now same relay's coil is fed by a separate 24V feed through the switch when it closes at -12C, thus the NC contacts open (cutting off the HP) and the NO contacts close diverting the "Y" feed to the auxiliary heat relay coil, closing the NO contacts there for oil heat.
That auxiliary heat relay also has a second set of contacts; these are NC and complete the "Y" feed to the compressor(these contacts open to isolate the compressor whe oil heat is on)
Hope this is clear.. I prepared a small schematic but could not attach here.
Louis B.

[KISS]

You probably can using "go advanced". Lots of options from pdf to jpg. If you nned to reduce the size of a jpg then use IrfanView - Official Homepage - one of the most popular viewers worldwide. Besides you have my email.

So, "Y" is used to control HP or Oil, based on -12C switch.
The aux heat in the tstat is unused.
A second safety assures that the compressor is off if OIL is supplying heat.

If HP is selected, the -12C switch can cycle the compressor without the required delay. If that -12C switch was instantaneous, then wind would make the compressor chatter. If it actually had some thermal mass, then it would not, but it would not be measuring air temperature.

Any specs on the -12C switch?

[LouisB]

You probably can using "go advanced". Lots of options from pdf to jpg. If you nned to reduce the size of a jpg then use IrfanView - Official Homepage - one of the most popular viewers worldwide. Besides you have my email.

So, "Y" is used to control HP or Oil, based on -12C switch.
The aux heat in the tstat is unused.
A second safety assures that the compressor is off if OIL is supplying heat.

If HP is selected, the -12C switch can cycle the compressor without the required delay. If that -12C switch was instantaneous, then wind would make the compressor chatter. If it actually had some thermal mass, then it would not, but it would not be measuring air temperature.

Any specs on the -12C switch?

Ok... you can go to the Hydro Quebec site specific for their Dual Energy Program using this link: Hydro-Québec - Residential Customers

Their pdf file on the outdoor sensor switch connection setup is attainable from that page (upper right); it is in French but you should be able to see the logic of the -12C control circuit. Note the leads going into the residence to confirm that the power rate is now increased from the approximates 14cents versus the 4 cents/kwhr.

I attach a pdf of the rendition of my control circuit.
Any suggestions are welcome..
LouisB

[LouisB]

Here is the final rendition of the control circuit.
This has been implemented with success.. works as intended.
If any questions, suggest you contact me by e-mail (brodeur.louis$sympatico.ca).. replace $ sign with appropriate symbol.
Cheers