Extension of: Fully Modulating Furnace, Regular or Communicating thermostat?
About a year ago I joined in a thread, which is now locked, called:
Fully Modulating Furnace, Regular or Communicating thermostat?
Its purpose (when it started) was to answer the question whether one should use a regular or a communication thermostat with a fully modulating furnace. I just then bought a York 100K fully modulating furnace and wanted to know if the "future" communicating thermostat from York would help keep my house in California an a rather constant temp during the day.
What we found out when we were able to talk with the designers of the controller at JCI was that setbacks completely messed up the controllers algorithm and it had to "start all over" every time a setback happened. The long and the short of it is that with setbacks on a normal - or even on their communicating - thermostat causes the system to start at low burn levels, and then quickly escalate up to max burn within 3-8 minutes after the first heat call after a setback completes. And this repeats for each new setback.
I found a way to program the York controller with a PIC chip to always stay in diagnostics mode and set the controller at 30% burn rate and low fan condition. This lasts only for 120 before the controller does an automatic reset and starts over. The PIC chip sees this happening and puts the controller back into diagnostic mode for another 120 minutes. This is a very primative and dumb way to get low furnace burn, BUT it does work and has no problems with 4 setbacks-a-day. I can share with anyone who wants how to wire and program the PIC, but it probably voids a warantee and you need a PIC programmer (which can be purchased for under 6 McDonalds burgers).
MY QUESTION IS: has anyone found a thermostat that will keep the York fully modulating furnace at a fixed burn rate? Is so, where can it be found, and does it allow you to set the fan rates as well?
POSTSCRIPT: I got "tagged" by the moderator a number of times for not "setting it and forgetting it". A nice mantra, but very costly. I have used the furnace for almost 1 year now. I live in Silicon Valley where the winter temperatures only get below freezing about 8 times a year and for only a few hours when it does occur. I need a furnace for only 6-8 months a year. I kept track of the daily temperatures over the last winter and used PG&G's SmartMeter to measure gas usage each day. I kept the furnace at 68-70 deg F during the day and set it back to 60 deg during the nights. Slightly different timing and temperatures for the weekends, but all are typical. By using setbacks from 11PM until 8AM during the weekdays (and almost the same for weekends), I saved over $600 in just gas costs. There would be a little more for electrical savings from decreased fan use. This just amplifys why the Federal Government MANDATES that all new public housing must have programmable thermostats: they save huge amounts of money and natural gas. So setbacks should be part of every new furnace.
Running extended times at low fire has at least a couple of draw backs;
1. Possible condensation in the primary heat exchanger, and
2. Low fire is the least efficient firing rate. IOW the thermal efficiency is much lower at the lowest firing rate.
Number one above will cause the heat exchanger to fail prematurely and number two just wastes your energy dollars.
How large a house do you have in CA that needs 100K BTU??? I'm in northern WI and very few houses need that large of a furnace.
Worry is a really gross misuse of one's imagination. -- PHM
If you have only had your mod furnace for 1 year/heating season. Then you can't say how much you saved using setback, as you have no way to compare it to not setting back.
I am a fan of setback. But you need a non setback year to make a real comparison.
And if a CA was used on that mod, you would see its combustion efficiency is lower at lower firing rates, the at higher firing rates.
In CA, I'd be shocked if the house ever gets to 60F overnight unless its' really leaky or poorly insulated. I doubt you'll see a lot of savings from setback since you're in a mild climate. I'm not sure how you're comming ot $600 in savings. I wouldn't think a furnace that size in your climate would even use $600 in gas total.. all season long.
My house uses about all 100kBTU worth of capacity combined between 2 systems and I don't expect it to need more than $1500 worth of gas for the whole heating season. I expect setbacks will save me around 10%. The average temps are below freezing for about 3 months.
You must have a HUGE house to need a 100k furnace in CA unless you needed a 5 Ton blower for the AC.
Programmable tstats have LOST their energy star rating because they, on average, dont save that much energy
not that big efficiency change
I am sad that no one has found a thermostat that can set the burn rate for the JCI systems...or maybe no one has responded.
How to compute the energy savings: for two months (DEC and JAN) I ran the system without setback. I also monitored the degree-day ratings from Moffet Field (nearby). This gives me a way to directly compare outside temperatures and energy usage for any time period. Then I started using setbacks as described. Since I have hotwater solar, very little gas is used for water heating and I estimated 90% went to heating (which I have indirectely verified). My average heating bill is around $350/mon with some going as high as $600/month. So the savings of $600 for setback is probably conservative.
My house is 35years old with a rebuild of a 2nd story about 15years ago with really good 2nd story walls, ceiling, and glass. But the 1st story is just "so,so". I have a big AC unit outside and indeed the condensor froze up twice in the summer because I did not have enough coil airflow. So the 100K BTU unit is big, but the need for the AC is bigger.
I remember in the conversation with the designers of the York full-mod system that we covered the change in efficiency from the 30% to the 100% burn rate. If memory serves, they said a 10% max change and that the peak efficency was in the 80% rate for my particular 100K system. They said that the air flow rate by the solid state motor controller is what kept their efficiency up at low rates. The biggest problem was the thermal conduction thru the ducting when you dropped below 30% (which is why they do not allow that).
I am confused on the condensation in the primary burner statement. I thought the York had all the plumbing for condensation removal and pumping it outdoors. Or is this something different. Please give some background so I can understand it, and possibly ask the York people to explain it in terms to unit lifetime conditions. If running a mod-furnace at 50% efficiency for its entire life would reduce its lifetime by say 40%, why would they make a modulating furnace in the first place? Something doesn't make sense here.
It is now two years since I started the original thread on controlling Fully Modulated Furnance and trying to set the burn rate to a low level. PG&E makes it easy to compute gas/electricity and now thermal-degree-days. Bottom line is that setbacks as I have described make a big difference.
But my real question, that no one has been able to answer: does anyone make a thermostat for the York series that allows the user to set the burn rate? Yorks fancy color LCD system allows you to set the fan rate, but not the burn rate. Does anyone know of a thermostat that can do that? Much thanks.
The main issue you have is 1 system doing a large 2 story house. Dividing the load between 2 smaller systems would have drastically reduced utility bills. How many times have you over cooled/heated one floor to make the other floor comfortable?
I'm not sure why you'd want to "outsmart" the thermostat and lock in a particular heat output.
IF you don;t allwo a modulating furnace ot modulate on it's own using a communicating thermostat, you might as well save yoru money and get a cheaper 2 stage furnace and regular thermostat.
This is how to keep it simple and still have a product that meets your needs instead of trying to look smarter than the whole hvactalk community.
Originally Posted by motoguy128
Not sure I understand all the new comments on "outsmarting the thermostat" and other comments.
I do have a large furnance because I need the fan flow to support the already installed AC load. As mentioned in previous threads, the AC can freeze up in hot weather because the flow should be larger. The city building inspector recommended that I go to even larger furnace to get even larger AC flow.
I am using three to four setbacks of temperature per day. Previous threads relate that designer of this furnace cannot deal with setbacks and that "all learning starts from scratch with a setback". I am trying in the wintertime to keep a low burn so that I get close to an 80% burn-on time in the house. Because of large 24' ceilings in main area, this keeps the air mixed and the overall temperature "pleasant". When I let the furnance go quickly up to 100% burn rate, I get very fast heat rise and the house becomes rather cold on the first floor becuase of the rather short 15-25% run times.
I use the "debug mode" of furnace operation to force furnace to go to lowest stage (I am told like 10-12% burn rate). This keeps the air-flow low and for the 2.5 hours this works, the 1st floor is quite pleasant and comfortably warm. I have tried to get PG&E's smartmeter readings during these times and it looks like my gas and electric bill are slightly reduced over the 100% ramp up mode. But the bigger factor is that the temperature says very constant for the 2.5 hours of low burn. That is what I am trying to get to happen during the 6-8 hour periods when I am home (more on weekends).
So I am trying to find a way to make the furnace stay in the low burn/low flow mode for as long as possible. My latest communications with the folks at Johnson Controls indicate that they are changing the debug mode to 95 minutes rather than current 150 minute mode. I am asking them if their fancy controller allows the user to control the max burn rate. Their answer is no. I am hoping someone will figure out their USB controller on the main board and allow user control of the heat section. If anyone knows of anyone doing this, please let me know.
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