georgo

what is your location?

I would immediately drop 09 down to 35 degrees and monitor HP's performance in keeping home comfortable. then make further adjustments as indicated.

I assume by having dual fuel, you have a favorable electric rate vs gas. you want to leveredge the less expensive electric against the more expensive nat gas.

IMO

I'm in central NC and you are right, I'm trying to use the heat pump more since it costs less to operate. I pay $0.095/kWh, $0.99 /Therm for gas.

I have the heat pump COP for 47F (3.92) and 17F (2.64).
According to this site: http://www.warmair.com/html/fuel_cost_comparisons.htm

My costs at 47F are:
Heat pump: $0.71
Natural gas: $1.04

My installer suggested 40F and 45F as good balance points (09) for the heat pump, so we used 45F last month and I wanted to try 40F this month. I just set option 09 to 40. If the gas rates increase next year, I'd be willing to try 35F.

As for option 08, I figured that if the outside temperature is even higher than 47F, there's plenty of heat in the air and less demand in our house so locking out the aux furnace at 45 or 50 would be a good way to save even more money. I just don't want to make a mistake and lock out the aux if it might come in handy for something else I don't know about.

georgo

I hate to disagree but based on your location/winter climate, a 40 degree setting marginalizes and defeats the purpose of having a dual fuel system. based on your calcs, HP heating on a BTU basis is 30% less expensive than nat gas.

I would start at 35 degrees and adjust accordingly based on comfort and HP operation.

just for info, I have my DF system changeover at 30 degrees.

IMO
Good Luck!

I would assume --

Option 8 (Auxiliary Lockout): If set to Of(f), the auxiliary will run whenever necessary to maintain tight control of the indoor temp, i.e. if the unit is running and the room temp drops below the setpoint (by apparently as little as 1 degree). If set to a specific temperature (i.e. 35), the auxiliary will NOT run (except during defrost) no matter how far-off is the indoor temp from the setpoint, unless the outdoor temp is below the specified temp.

Option 9 (Heat Pump Lockout): Set at Of(f), the compressor (heat pump) will always run (with the auxiliary) no matter how low is the outdoor temp. If set to a specific temperature (i.e. 35), the compressor is locked-out and ONLY the auxiliary will run when the outdoor temp drops below the specified temp.

I don't have a heat pump lockout on my thermostat, but I have an auxiliary lockout which I have set at 25 ... meaning my auxiliary pretty much never runs.

tigerdunes, I decided to give 35F a test. Temperature at the register is about 84F, which is about 5-6 degrees lower than what it is when the heat pump is running at 40F. I'll try this for a few days and see how it goes. I was trying to avoid defrost cycles, just to prolong the life of my reversing valve. The air temp is a little cooler than what we are used to, so the rest of the family might not be a fan. ;)

Do you have an opinion on option 08, the aux lockout temp?

dadoes--I agree with your take on option 08. I would like to lock out the aux gas furnace at 45F, so it won't run at any temp above 45F and just force the heat pump to heat up the house (with the exception of defrost cycles, which use aux heat no matter what the lockout temp is). Seems safe enough to me, but I'm not in the HVAC business.

that is pretty inexpensive electric. I think 35 is a good switchover temperature to gas. You could go 30. When you measured the temp as 84degrees fahrenheit at 35 outside I would have expected higher 80's. Maybe it just started to cycle.

If you have the option on your thermostat for number of cycles per hour you may want to consider switching to least amount of cycles per hour - 1. Your t-stat probably does. It sounds very similiar to mine with the 5 degree increments.

Is your house newer and well insulated? Heat pumps do a better job at maintaining if the house is tighter. If its a drafty house 35 would probably be the lowest. you could do comfortably.

I think you can lock out your gas at 45. Heatpumps kick-but at those kind of temps.

Whenever it is snowing or sleeting I prefer to switch to emergency which is gas. I'm not a fan of when the heatpump is defrosting alot.

I'm in the Triangle with a Carrier dual fuel system. Do you have an Infinity system? I'm just curious since I don't have the COPs.

I have my switchover set at 35 degrees with pretty similar rates. I'm with you on avoiding defrost cycles. I think I had guessed the economic balance point in the 30-31 range so 35 seems like a good idea. I suppose it might cost $20 a year vs but that seems worth it.

No problems here on the temp from the vent. Ease the family into it. Set at 38 and walk down slowly.

Just an argument for higher gas use - the extra airflow on a heatpump makes for higher duct losses. The COP doesn't take that into account. Even a new house with r-8 ducts and mastic sealed has duct losses. Our energy audit put it at over 10% which I found pretty surprising.

david_cary: We live in the same area, I'm in Raleigh. I don't have an Infinity system, though. I've got a 25HBC5 base heat pump, performance boost 90 furnace, and edge thermidistat. I had to stretch my budget to get all of those, plus all new, correctly sized, sealed and insulated ductwork. All I really needed in the beginning was a new AC and new ducts, but rebates and credits removed $2600 from the total cost of the complete. It's hard to walk away from that kind of deal.

As for the COP, I got them from a product data PDF from Carrier. I found the AHRI number of my system and it listed the COPs. Do a google search for your heat pump model and you might find it, or you can ask Carrier for the sheet. I'm sure they'll provide it. I wish that it had the COPs for temperatures in the 40-25F range.

neohioheatpump: The register temp stayed at 84-85 the entire time. The run at 35F was pretty long, too. I started to worry that it would never end, but it did. It didn't immediately start again after it was done, so I think the heat pump can keep up at that temp. If it doesn't, 40F it is. As for my house, it was built in 1981 and isn't tight, but it isn't overly drafty either. Insulation levels aren't bad, but I could benefit from more and will probably add some in the years to come. This year I blew out my energy budget on the system and figured I will have to do that project later.

I am curious if you setback your thermostat during the night and when you are out of the house. If yes, how much of a setback do you do and how long does it typically take to recover with the heat pump operating by itself when the outside temperature is around 40F?

I would lock the gas out at anything above 40 and lock the heat pump out below 35 and then try 30. So if the temp is 40 degrees or warmer heat heat pump does it all. When the temp drops below 35 the heat pump is off.

The beauty of this is if gas prices go sky high again you have the option of letting the heat pump run on down to whatever temperature you choose. I would have to say even if the temp was down in the teens your heat pump should be able to handle it with only a marginal amount of back up bu the long times would of course be longer.

I am all electric so I let the heat pump run on down to 10 degrees and use the heat strips in stages to give a momentary boost as needed which even at 20 degrees isn't very often. I also have the strips locked out at anything above 35.

With the outdoor temp sensor and setbacks the thermostat will learn how the system works at different temps and how the house recovers at different temps and starts the recovery process depending on how much setback and what the outside temp is.

One other thing that can make life with a heat pump or furnace more comfortable is a humidifier if the humidity is down in the 20's even getting it into the 30's makes it feel warmer.

I'm curious for comparison, what is your house size and what was your Dec bill? Gas and increase in electric over October. My gas bill was $60 and electric increase about $50. I was surprised to use gas so much and obviously it was cold. But I actually used the same gas last December.

I do have a 4-5 degree setback overnight and during the workday. Overnight is 68, workday is 67. When we are home, we keep it at 71. I don't know how long it takes the heat pump to recover because the last month has been so cold the furnace has handled all of early morning recoveries that I am aware of.

I'm still on the fence about the size of setback I need to use., here's why: In Dec 2009, we used 90 therms of gas with our 80% furnace. We kept our stat at 68 when we were home and let it drop to 66 overnight and 60 during the workday. In Dec 2010, which was about the coldest Dec I can remember, I kept the stat at 71 during the day, 68 overnight. We used 70 therms of gas and I estimate about 200 kWh more electricity. So we were warmer and used less gas with the hybrid system. Certainly most of that was caused by the higher efficiency systems, but I do wonder what role the smaller setbacks played.

My house is single story, 1700 sq ft.

I am going to guess your recovery time has been short since in the past the auxillary heat (furnace) was not locked out. In the past when did the auxillary heat kick in? Was it a staged timer whenever the heat pump could not satisfy the thermostat demand?

The dual fuel system has a few variables to play with in order to achieve the optimum set up. With a little trial and error you should find what is comfortable and economical.

georgo

a couple of opinions.

I don't like HP setbacks more than three degrees and even at that you should monitor how HP operates on low end of the changeover temp and length of time for recovery.

the 84-85 supply temp at/around 35 degrees seems on the low side. you might want to take additional readings. I would not be overly concerned but I would get refrigerant charge checked on next PM.

the mention of defrost calls makes a strong case for electronic demand defrost and I would not purchase a HP with time/temp method. In fact, I don't understand why the manufacturers have not figured out a cost effective method of defrosting a HP condenser without blowing cold air into a home and tempering the air with heat strip or gas furnace backup. how inefficient can you get.

if you have CPH setting, I would not go lower than two.

as far as gas furnace operation, that's up to you. I do want the ability and choice to switch to emergency anytime to run the furnace.

IMO

mike_home: The aux heat usually kicked in when the heat pump was locked out or when we wanted to raise the temp in the room. Now that it's locked out at 45F, I'll have more time to observe the behavior.

tigerdunes, very impressed with the observation on the refrigerant charge. The tech measured it during the start up and while it is low, it is exactly in spec for the temperature in which he started the system up. He stated that he will fully charge it during the spring PM, when the outside temps are 75F or more.

I left the CPH setting to 4.

The thermidistat offers the ability to switch to gas furnace at any time by simply toggling the mode to Em Heat, so I have gas whenever I need it.

As for the time/temp method, I'm sure that is what my HP uses. It's certainly not the best method. When I chose the hybrid system, my desire wasn't to switch from gas heating to full heat pump, it was simply that it cost $200 more than just an AC & furnace and provided two fuel options to counter future price fluctuations during the wintertime. I got the model that I could afford and that would qualify for credits and rebates.

georgo

you have a very nice system.

I wasn't being critical of your HP.just on my soap box about HPs and defrost. surprised that Carrier has not gone to electronic demand to help eliminate/reduce the unnecessary and expensive defrost calls.

I would drop CPH to at least three.

IMO
Good Luck!

No worries, I didn't take it that way. Reread my message and it sounds more touchy than I felt when I read it. I've read enough of your posts to know you are professional in all of your correspondence.

Why the CPH drop to 3?

tmgeorgo

well, on the CPH to three,you get a little longer run time which should be more comfortable to your fam especially moving down to 35 degrees. not as a big deal in heating, would be in cooling. you don't want shortcycling. any idea of current average run times?

yes, I know about one's family members and HPs. lots of variables there if HP heating is new to them. LOL...

another thought. your defrost timer is set to how many minutes?

IMO

"Temperature at the register is about 84F, which is about 5-6 degrees lower than what it is when the heat pump is running at 40F."

That is right at the critical point for comfort.

84F moving air feels cool (anything much below about 98 F actually).

If you do not mind the 'cool draft' feel, go for it.

I was getting 91.0 F vent temperature with inside air temp at 68 and outdoor at 34F. Outdoor humidity was only 48% so it was ideal night to run the heatpump. It was never going into defrost.

Keep in mind, I don't have the highest fan setting on. I"m using the 2nd highest of the 4-speed air-handler.

I used to use the highest fan setting because I thought lots of airflow was good but I discovered it was kind of noisy. I prefer this much more.

CPH can be 2, 4 or 6, so I'll keep 4. I can always come back and adjust that later, if we aren't happy with it.

The smart recovery option is set to 90 mins.

If I recall correctly, the defrost timer is set to 90 mins. I can't confirm that without asking the installer and there doesn't seem to be a way to change that from the thermostat.

I think the 84F air temp was a little too cool for us, so I'm going to revert to 40F. After the system is fully charged in the spring I'll try 35F again next winter. The heat pump is already running at temps slightly lower than 40F since the outdoor temp sensor can vary by 1-3 degrees from the actual outdoor temp.

georgo

well, I hate that you are raising the changover back to 40 but certainly respect your decision. It does marginalize dual fuel operation from an operating cost point of view as well as your extra investment in the HP condenser over a straight AC condenser.

when was your new system installed? while the installers are supposed to have their charging charts, it can be problematic if charged at cool temps. your last post indicates installers will be back in spring.

several suggestions.

1.system charge should be checked at minimum 70 degrees outside temp. I find that 84 deg supply air suspect.

2.defrost timer should be at 90 minutes and installer should show you how to adjust as needed.

3.fan setting should be checked as suggested in post by neohio

4. if stat does not have 3 CPH setting, I would try 2 CPH now.

I can't recall-is your furnace sgl stage or two stg?

you are correct. these outdoor sensors can have a wide tolerance + or - due to many factors including wind, shade/sun,etc.

IMO
Good Luck!

whups- called the installed=called the installer

No worries on the 35F setting, I'm going to use it next year, or maybe even later on in the winter when it isn't as cold all the time. I'm fully aware of the fact that it will be cheaper to run the heat pump down to 35F, but also don't want the feeling of cool blowing air in every room. At 40F, the register temp is 90F, which isn't bad. Perhaps it'll be even higher when the system is fully charged.

1. The system was installed in late November 2010, just in the nick of time to get the credits. It's only gotten colder since then. Outside temps haven't been above the 50s since the install.

2. I confirmed 90 mins defrost with the installer. They're a great company, I'm sure they will show me how to adjust that if I can get to it.

3. I didn't know there was any option for fan speed in heat pump mode, ours simply runs in high at all times. I'll ask about that.

The furnace is a 2 stage but does not have a continuously variable speed blower. The comfort heat technology uses less gas and a lower fan speed, and it uses that mode pretty much all of the time. The only time it doesn't is when its recovering from a temp setback.

Update: Installer is going to check and probably reduce the fan speed in heat pump mode so the temperatures coming out of the ducts will increase. Once that's done, I'm going to switch back to 35F.

georgo

that's a good deal if your setting is on high. you would immediately pick up a few degrees.

and I would change CPH to 2.

let us know how this works out.

IMO

Fan speed was reduced today. Tech stepped it down one notch, from high to medium high (there are five speeds). I lowered my heat pump balance point from 40F to 35F. I also lowered the aux temp lockout from 45F to 35F after we both witnessed it using aux heat when it was just maintaining the setpoint, not trying to recover. Tech's recommendation was that I keep CPH at 4, so I did.

Anyway, register air temperatures in heat pump mode are about 4-5 degrees warmer now, which is much better. No one is complaining about being cold. :)

To review everything that was discussed in this thread:

Option 08 = 35
Option 09 = 35
CPH =4
All temperature setbacks are only 3 or 4 degrees.

Now I'm going to leave it alone and see how the bills look after the next cycle.

Just a thought. Setback further. You get a pretty big advantage from setbacks. At 35 degrees, NG and HP and within 10% of each other. So you gain more advantage by setback than you might lose by running NG. In fact, being able to setback is a big advantage of NG.

Example. 60 degree setback at night for 8 hours. So my walls are only facing a 30 degree difference with the outside overnight instead of 40. That is 8 hours at 25% less heat loss. Then at wakeup, I run my NG to get it back up to temp - paying perhaps 10% more on average (let's say it is exactly 35). And that is just for the few minutes it has to run. There is a lot more to it. But the reality is that, you'll use NG most mornings because of temp anyway - so the setback only helps.

Daytime setbacks are less helpful because the outside temp is higher. Most stats will keep you out of aux heat with a bigger setback I bet - but that depends on a lot of variables especially how big your HP unit is.

My takehome is that aux heat when it is NG is not to be feared. A setback beats the small cost premium of NG most of the time.

I agree with that, setback's are no problem if backup is natural gas. The less heating load, the less energy being used. Obviously if your out of the house for only 3 hours and put down the t-stat and then turn back up when you return you not going to save much or any.

OK, I'm open to that.

If options 08/09 are the same, 35F, the gas furnace really isn't available as a option to restore from a setback over night unless the outside temp is below 35. In that case, the heat pump starts about 90 mins early and works its way backup. Good for economics, but bad for fast recovery. Like you, I'm not scared of using NG and think it would be better for setback recovery. Carrier thinks so too, the edge manual says that option 08 defaults to OFF so the system can use NG anytime it wants to heat fast.

So today, I'm at home all day and am doing an experiment. I have the heat pump locked out at 35F (option 09) and the gas furnace locked out at 45F (option 08). This is the way I'd really like to have it.

When trying to recover from setbacks, the Heat Pump isn't used much at all. In fact, it sounds like it starts up and runs for a short time, then quits and the gas takes over.

After it has recovered from setback and is just maintaining temperature of the room, the heat pump and gas furnace are taking turns on alternating runs. This behavior is baffling to me. Once cycle is gas, the next heat pump. Over and over. It seems very inefficient. It should be heat pump only. That's the most cost effective thing to run. Why is it behaving this way? I have searched every HVAC posting on the web that I can find and haven't found an answer. One idea I had was that the inside temperature of the house dropped 2 degrees and the next time the system called for heat, it chose the furnace. Then the furnace gets the room nice and hot, so the next time the heat pump is used. That's the only reason I can think of. If someone on this forum is a carrier expert and can weigh in on this, I would greatly appreciate it.

Lewstone: I missed your postings earlier but I'm curious what the installer specifically did to adjust your system. Do you have that information?

Just as a point of comparison, my option 08 is at 45.

Is it possible that your stat is set too low on cycles per hour? I didn't have NG run during the day yesterday. My other thought, is because of the wind, your heat pump couldn't really keep up even during the day.

Of course, yesterday was a tough one - lots of wind and just above 35 degrees with marginal sun.

CPH is set to 4, what are you using? And what are you using for option 09?

I'm going to leave everything the same today and keep an eye on it.

I might be confused on 08/09. But gas always on below 35 and heat pump always on over 45.

Don't remember my CPH.

We are the same on the lockouts, gas only under 35, heat pump only over 45. And unless you changed the CPH, it defaults to 4.

Temps have stayed low and my heat pump hasn't been on, so the experiment is still on going.

In the interest of science, I tried moving the heat pump lockout from 35F to 30F. Everything was fine, the heat pump ran for a little 10-15 mins and the temperature of the air at the register was about 84F, but then it stopped and the thermostat switched to aux. The outside temperature was 32F. I guess my heat pump would've asked for help from the electric strips, if it had any. Since it didn't, it switched to gas. That suggests to me that 35F is about as low as I'm going to be able to go, at least until my system is fully charged in the spring.

No problem and I appreciate you being ok with me bumping into your exchange here- I am following this with alot of interest. Just quickly, on my issue, the installer came back out. At first he said this was normal as shared earlier and had to be told (from a non-expert) that this was not normal at all. It seems that he made some type of wiring adjustments (unknown since my wife cant follow any of this when she was watching and asking) and then adjusted settings within the setup of the Edge Thermidisstat. We are currently running oil heated-water baseboard as the backup and then the Performance series HP system (EER 12.5, SEER 15.5 and HSPF 9) cant find the AHRI# handy. Temps have been consistently at between 28 and 34 degrees here in Viginia for the last 5-7 days. We are having to manually switch from HP to the oil heat system for right now since I dont want this installer messing with anyting else to connect a relay that allows both to be working from the one thermostat. I will do that later (hence reason for following this discussion closely) I am tracking kW useage off the meter. Here's what I am seeing:
Set the HP Edge at 68 degrees and it holds house temp steady wihtout having to use AUX at all.
Set the oil heat-boiler at 66 setpoint(manual)
It seems that only infrequently will the boiler kick on to augment the HP (running simul right now)

Energy useage has been between 3.12 and 3.77 kW per hour across last 5 days (taken in 24 hr periods). VaPOwer is at about .06 cents per kW right now I think, so I'm looking at what 744 hours per month at avg 3.44 kW (.20 cents) per hour= $153.00/month.

This is for a brick ranch, 1820 sq ft house

Lewstone: It sounds like your situation isn't the same as what I'm observing, all of my changeovers are automatic and done smoothly by the system.

For the others who are following this thread, I haven't figured out why the system flip flops between my heat pump and gas furnace when the temps are between 35F and 45F. The weather has warmed up a bit so I have been able to observe it again, but I'm never around the house long enough to observe it for hours at a time (which is a good thing ;).

The flip flopping behavior stopped when I changed the heat pump lockout temperature (option 09) from 35 to 40. I'm going to leave it there and continue observation.

I will repeat my attempts to set the lockout to 35F next season, when my heat pump is fully charged.

How do you get to the thermostat control configuration options? I would like to reset option 08 so my oil furnace takes over at 35 degrees.

Start your own thread.

This is an old thread. Piggybacking is not a good idea and you will get better results and help with a new thread. Include all details of your system and type thermostat.

IMO

I have a heat pump system installed in 2001 with existing oil furnace that was installed in the 1960's.
I'm thinking I need to re-set the 38degree switch-over because of fuel costs nowadays. I've read several posts on this site and have concluded it's a good idea. What is a good switch-over point nowadays based on current cost of elec. vs. fuel? I live in NC mountains and it gets about 10 degrees colder here in the winter than in the coastal areas. I was talking to a HVAC tech who says he's got his newer style h.p. w/gas system set at 25degrees. This may be a little too low for me, but I am thinking I can improve on mine.
1. What are your suggestions on the switch-over point?
2. I have a now-discontinued Carrier t-stat which I think may be a TSTATCCPDF01-B as best as I can tell and don't have the manual that shows me how to set the switch-over. I'm pretty sure I've got the adjustable kind but I don't know how to reset it by the keypad since it just shows home user buttons. I can't get past this point. The tech says I can adjust it if I have the manual. The manual was never provided by the installer. Any one got this style and can help?

joynerz,

You may want to read the post immediately before yours.

Please Help - I have a heat pump with a electric furnace. I have a Honeywell System VisionPro TH8320WF - I have a a question about the Heat Pump Compressor Lockout and Heat Pump Aux Lockout. The Heatpump works great - however when the Aux is supposed to come on and work it doesn't once the temperature outside gets like 27 degrees and that's when I need it. I woke up and it was 58 degrees in my house. I was freezing. Any suggestions on what I should be doing?