Hi, I have a water source heat pump with water coming from a cooling tower. I have a single stage duct-mounted electric heater in the discharge duct. My Nest is working fine in heat pump mode for both heating and cooling modes. Aux heat wire is set up. When the outside air temp gets below 40 deg., the heat pump heating does not produce enough heat and I want my electric heater to turn on. My electrician verified that power is delivered to the electric heater, but the mechanical contractor never hooked up the heat strip side. Before that is hooked up, I need the following question to be answered
My question: When the outside temp is 40deg F or below, I need the compressor to turn off, the fan to run, and the electric strip to turn on. Due to the electrical supply, both compressor and electric heat cannot run at the same time. I want to verify what Nest settings will allow this sequence. Below is my heating wiring. Thank you,
The power for the heat pump compressor should be on a separate circuit breaker than the air handler (with the electric heat coils).
But if you do not want the heat pump to run when electric heat coils come on you will probably have to tell the Nest you have a "dual fuel system" and set a lockout breakpoint temp that it switches to the electric heat coils only.
Aux heat is designed to run with the heat pump at the same time so you have to change the system type in the Nest setup if you dont want them to run at same time.
Emergency heat is different and you have to manually turn it on so it will not work automatically like you want it to switch at a certain lockout temp.
So you can try the dual fuel system type and pick the lockout temp it will switch over to electric coils.
There should be a terminal screw in the air handler for the W wire to connect that triggers the coils to activate and there is usually a set of breakers inside the air handler dedicated for the coils so maybe they are off. Or he did not hook up the white wire.
@Houptee Thank you for your answer. To re-cap, I will change the system type to "dual-fuel" and set a lockout temperature setpoint. To clarify, the W wiring to the thermostat set on Aux (the way it is now in the picture is ok), and the white wire from W will connect to the relay in the electric heating coils (there are no breakers in the AHU for the electric heat). Does that sound right?
@Houptee As a follow-up, I set it up for dual fuel and set the changeover setpoint. During the Pro TEST, the heat pump heating and heat pump cooling tests were successful. However, when testing the Alternative Heat, the electric strip heat came on, but the fan did not come on (I kept it testing about 3 minutes before stopping the test). How do you set it up so the Fan and Alternative Heat come on in Alternative Heat mode? I also wonder if the fan will keep running a couple of minutes after the heat strips turn off so they are cooled down by the moving air... Thanks again for helping. Much appreciated.
I was thinking about it and might not work with a jumper because if the G gets power in AC mode it will apply power to W also and turn heat strips on in AC mode.
I would need to see the wiring diagram for the air handler.
Usually when you take the cover off the air handler there is a decal on the back of the cover with the wiring diagram and it shows Thermostat wiring as "field wiring" and the terminal screws etc.
Like I said earlier when you add electric heat kit to air handlers they usually come with a bracket and circuit breakers dedicated to trip inside the air handler if the heat coils shorted. Also depending on the KW of the kit it dictates the wire size needed coming from the main electrical panel to the air handler. So not sure why you cannot have the heat pump run with the electric heat at same time in the Aux setup since the air handler has its own dedicated 220v breaker and the outdoor unit has a dedicated 220v breaker and they should both be able to run at same time.
How old is this system and what brand and model etc?
Good feedback. The unit is a Climate Master WSHP Model TCV042AGC30NLTS 208/1. Both the WSHP unit and the electric duct heater is connected to the same 40A circuit (the Addison unit it replaced had the Aux EH inside the unit). I attached the two photos that may help. The EH-1, EH-2 and 24v connectors for heater in the wiring diagram are shown with the orange arrow. The control wiring to the Nest is shown by the blue arrow. The wiring to the "typical wiring block" has the purple arrow pointing to it. Hope that is helpful.
@Houptee As a follow up to my previous reply, I thought these additional pictures would also help. For the Elect Duct Heater, the white control wiring is connected to the Red wire that turns on/off the heaters. The Nest test confirms Nest is turning on the EDH relay.
P.S.: I know the light blue EDH heater wires are not connected. That was how the A/C contractor installed it and I want to get the fan running first before the blue wires are hooked up.
I think to get the air handler to kick on the fan you need to put the White wire from Nest to the W on the air handler, and run a wire from W screw up to the Red wire for the electric heat relay.
So then 24v signal from the nest for heat goes directly to W on air handler and jumpers off to the relay up top. Both energize at same time.
The logic in the air handler board should know to turn on the fan with a call for heat on W.
Hopefully since you set up the Nest as dual fuel it will not trigger the Y and O wires so the heat pump wont turn on the compressor during a call for heat below the lockout temp.
You would have to test it to confirm.
@Houptee Thanks. Before I called an A/C tech to install a jumper, just tried something else that got the fan going.
I clicked Equipment, Settings, Done, Heat Type, Pro Setup, and Continue.
The backplate graphic for each of the wires showed up. I rotated the dial to the Waux and pressed to select (I didn't know you could do that before now). I rotated the dial to Source and select, then selected Electric (It was on Oil) and pressed the display. I then rotated the dial to Delivery and changed it to Forced Air (it was on Don't Activate).
Then I tested the Auxiliary Heat and the fan and electric heat relay activated. So the Nest controls as wired worked with this settings change.
My problem is solved - and thank you VERY MUCH!
Ah ok I thought you already had it setup as forced air heat.
So I guess the W input is not needed since the Nest knows to just trigger the G fan wire on now along with the white heat that you have directly to the relay.
Awesome you discovered it was just set up wrong!
What part of the country are you in? I have not seen this type of water source heat pump yet in NJ.
In New Symrna Beach, FL at our 12 story condo. We have 55 of these units connected to a cooling tower. Very efficient in cooling and heating mode. It doesn't get below 40 in central Florida often, but when it does, there isn't enough heat in the water for the heat pump, so aux heat is required.