Dual fuel control methods - pros and cons
This is really a general question about the relative merits of dual fuel control methods, not really a question about a specific system.
We know about the tried-and-true method of using outdoor temperature to decide to use heat pump or aux heat. We also have seen some of the newer methods implemented by White-Rodgers and others, that do not use an outside temperature sensor at all, but use some sort or proprietary algorithm to decide.
You can see some youtube videos from White-Rodgers on theirs.
What has been your experience with these, good or bad? What has been customer satisfaction you've noticed? How well do they each work? Is one better at comfort and one better for economy, and why? Pros and cons of each?
I think that communicating systems are going to be the future of this. I don't know much about other manufacturers but the Trane XL20i with indoor communicating air handler or XC80 or XC95M will talk back and forth and measure how well the heat pump is keeping up at heating the house and can switch from one source of fuel to another based on the electric and gas rates you input into the XL950 thermostat. They use EEV's instead of TXV's to be as efficient as possible.
Now, make it WiFi so it can get the rates and adjust automatically, then I'm in!
Originally Posted by SkyHeating
For the time being, I'm interested in a comparison of the 2 ways - 1. using outdoor temperature, or 2. some internal algorithm, to decide when to switch.
If you are using a dual fuel system with a multi-stage furnace (ie: heat pump with 2 stage gas heat), then you can achieve optimal indoor comfort no matter what the outdoor temperature is. The switch over point between a heat pump and gas heat can be based on comfort (ability to maintain indoor temperature at a constant) or based on cost (a tough thing to accurately calculate because of the various factors that one must take into account such as :
1) ability to maintain set temperature
3) outdoor temp
4) indoor humidity
5) actual efficiency of heat pump/gas furnace
6) sunlight/solar heating effects
7) temperature of objects in rooms
8) airflow of system
And a lot of other factors
I think you hit on something. I believe the White-Rodgers algorithm for doing dual fuel without an outdoor sensor is biased towards comfort. Actually, any dual fuel controller that doesn't use outdoor temp would have to slanted towards comfort, because the switch-over temp won't be based on the cost of fuels. All it knows is how long it took to reach the setpoint last time, and the temperature differentials (previous and current).
When you use one that does use outdoor temperature, I think you're most likely to interested in economy.
I have an Emerson E-Z read something or another. The first winter I just let it do it's thing and make the switch on it's own. On a calm night it would switch to gas at around 8°F. Sometimes it would run on gas for a couple of days if it stayed in the teens.
Last year if it was in the teens and calling to drop down to 10° or lower I would switch it when I headed for bed myself. I had my knees replaced and I sleep better when I'm toasty so I'm good with the warmer air from the gas furnace.
I have never had a complaint with the setup I have. I was a little surprised once when it had switched on its own and had been on gas all day that it switched back to HP when my wife had the oven going in the evening.
One thing to keep in mine is I enjoy some pretty low electric rates, what works in my world wouldn't be the best plan in others.
The Trane XL950 is wifi
Originally Posted by garya505