Simple control, maybe?

[jchaters]

Hi I am looking for help on a small control setup. I want to marry a hydronic heatpump (air to water) with a gas boiler. The scenerio is as follows. I would like the heat pump to operate from 11 Pm to 7 Am and the boiler to operate from 7 AM till 11 PM. The Heat pump output water would be between 130F and 150F degrees at all operating times. If the temperture output of the heat pump was to drop below 130 the boiler must fire up to supplement the heat pump. If the outdoor temperature was to drop below 10F the heatpump would shut down and the boiler would supply all heating. I think I am looking for a timer with an outdoor reset and an aquastat, but not quite sure. The application is for Canada where smart meters are about to become reality. Electricity will be very inexpensive at night and very expensive in the day (3 cents/KW at night 12 cents/KW in day) Thus a heatpump with a COP of 2.5 or better will run for much less than natural gas overnight as long as the temperature is not too low. Thank you in advance

[crab master]

Simplest solution a programmable logic controller. I am sure you could do it with relays and sensors but just briefly thinking about it, it would get pretty complicated in a hurry.

Question for you is what kind of head pressure are you running on the heat pump to maintain 130 deg plus water output from the heat pump? Also what refrigerant are you running?

[jchaters]

Hi and thank you for your reply. The refrigerant is currently 407 but will be switching to 410 in a few months. The product is from Italy

[jchaters]

Hello again. A direct link to the Heat Pump is at http://www.aermec.com/prodotti/default.asp?id=133&ftype=achiller&sun=an

[crab master]

To me that seems like you would be running an awful high head pressure to maintain the 130 deg F plus loop temp but if the unit is rated for it great.

Also what area in Canada are you in? Just curious as I am about 2 hours from the Canadian border - North Idaho.

On the controls you are speaking of I would say you would also want a user interface either a small operator panel with a screen or something you could connect to your PC/laptop. This would be so you could make set point modifications and other mods as needed

[jchaters]

I am located in Toronto. In two years or less we will be on Smart meters. Hydro today is 5.5 (plus debt retirement charge etc) cents/KW but will be going to 2.9 cents per KW on weekends and nights. In the day time it is going to double. Thus people are looking to heat electrically again during the lower cost times and use gas during the week days.
The electric heat pump option will be much cheaper than gas at times. Thus the controls issue. Thanks Jim