EcoRenovator - View Single Post - Designing a General Purpose Heat Pump Controller

jeff5may · 11-16-14, 10:17 AM

This is exactly how I'm doing trials on my dirt cheap window shaker. I repurposed the power board out of a portable dehumidifier/ac unit that will end up as some sort of heat pump someday.

The board in its old home

Now it's imprisoned here:

The arduino gets its power from the 5V regulated supply on this board. I cut up a usb cable (blue) and soldered it directly to the 5V rail and its ground. The breadboard has status LED's on it for the compressor, fan, and reversing valve outputs. The yellow and green wires from the breadboard tie directly to the relay buffer IC inputs.

I lifted the power board's mains fuse to separate the relay contacts from the 120 VAC input, since my window unit has contactors and a defrost board in it that run off 24VAC. The 120VAC is run through the onboard power supply and comes out with unregulated 12VDC for the relays and regulated 5VDC for the buffer IC (and no longer attached stock control board) and arduino.

When I originally rigged the window unit, I used a non-heat pump thermostat, so I had to wire it up "weird" to make it work. To interface with the controller, I ran two phone cords since all I have close is single-pair phone cords. The red wire runs 24VAC power to the relays on the power board using one cord. The other carries the normally open relay contacts back to the window unit. Since the unit has a defrost control and it's heating season, I am not running the reversing valve output back to the window unit.

As of today, the controller operates with a 2 degree deadband in heat, cool, and auto-changeover modes. I haven't integrated short-cycle protection, defrost sensing, or serial comms yet.

I hope to release a beta version soon that will function as a wall-mounted thermostat does. It will have lots of "dead" code in it, with variables that do nothing (yet) and extra menu items that can be filled in for future functionality.

This is the first full weekend I have had off since sometime around the fourth of July, and the powers that be say overtime will die down until after the holiday season. If I can complete this task and the other 20 in front of me before Valentine's day, that would be awesome!

11-16-14, 10:17 AM	#275
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,428 Thanks: 431 Thanked 619 Times in 517 Posts	This is exactly how I'm doing trials on my dirt cheap window shaker. I repurposed the power board out of a portable dehumidifier/ac unit that will end up as some sort of heat pump someday. The board in its old home Now it's imprisoned here: The arduino gets its power from the 5V regulated supply on this board. I cut up a usb cable (blue) and soldered it directly to the 5V rail and its ground. The breadboard has status LED's on it for the compressor, fan, and reversing valve outputs. The yellow and green wires from the breadboard tie directly to the relay buffer IC inputs. I lifted the power board's mains fuse to separate the relay contacts from the 120 VAC input, since my window unit has contactors and a defrost board in it that run off 24VAC. The 120VAC is run through the onboard power supply and comes out with unregulated 12VDC for the relays and regulated 5VDC for the buffer IC (and no longer attached stock control board) and arduino. When I originally rigged the window unit, I used a non-heat pump thermostat, so I had to wire it up "weird" to make it work. To interface with the controller, I ran two phone cords since all I have close is single-pair phone cords. The red wire runs 24VAC power to the relays on the power board using one cord. The other carries the normally open relay contacts back to the window unit. Since the unit has a defrost control and it's heating season, I am not running the reversing valve output back to the window unit. As of today, the controller operates with a 2 degree deadband in heat, cool, and auto-changeover modes. I haven't integrated short-cycle protection, defrost sensing, or serial comms yet. I hope to release a beta version soon that will function as a wall-mounted thermostat does. It will have lots of "dead" code in it, with variables that do nothing (yet) and extra menu items that can be filled in for future functionality. This is the first full weekend I have had off since sometime around the fourth of July, and the powers that be say overtime will die down until after the holiday season. If I can complete this task and the other 20 in front of me before Valentine's day, that would be awesome!