OT---Central Heating System

I moved into a home about four years ago. It has a Carrier Heat Pump (Puron)? and it is about 12 years old.
When looking at the home, before buying, I noticed that the emergency heat was cutoff at the unit (external mounted breakers) I asked the owner and he stated that they had not had a situation where they needed auxiliary heat??
He had the new unit installed and heated the home, even with the temperature in the teens!
I have a limited knowledge with heat pumps but always thought that if the thermostat wasn't satisfied in a certain length of time, the auxiliary heat would come on.
During the first year I lived here, I turned the auxiliary heat on and turned the thermostat up to max. I felt and SMELT the heating strips.
My question is --how can a heat pump create enough heat when the outside temperature is in the teens without using auxiliary heat strips?

It will be sized down to a certain temperature, below that it cannot pull enough heat out of the air and needs the strips.

They can"t, it"s that simple. Do not listen to an
energy expert from the electric company.

"My question is --how can a heat pump create enough
heat when the outside temperature is in the teens
without using auxiliary heat strips?"


Contact a heating contractor in your area regarding
the best type of heat to use.

Heat pumps have become popular up here in Minnesota, they
are really cheap to operate.

Very expensive to instal tho.

Of course here we run many loops of pipe in the ground 7 feet
deep, and use the 50-55 degree ether to pump the heat from.
That's where all the expense is.

Paul

Hi, will attempt to offer you my knowledge about heating? This past August we had a heat pump installed for $7,100.00 taxes included. We have alway's heated with wood and oil fired furnace forced air. The heat pump was hooked into the plenum of our furnace and whenthe temp drops to below where the heat pump can get heat from the air, then the oil furnace takes over, everything works very efficiently. Being as I had a few cords of wood, continue to use wood at my convenience. When purchasing a heat pump a reputable dealer will tell you when the temp drop's to, say -12 C the heat pump cannot supply for the demand, then something else has to take over to supply the heat. I also had installed electric heaters a few years ago, they are alway"s turned off. The place where we live, usually get a couple of months where it get's cold and windy. Might be places where the temp would not get that cold. So there are a lot of differences as to age of house and insulation being used. Cheers, Murray

Geothermal is the way to go if you use a heat pump. That system here is about $15,000 and up.

Two days ago, overnight temperature here, was 7 degrees! I heat my 3200 sq. ft. home with two unvented NG log sets with blower motors. Both gas logs were set to maximum setting on Low.
Home temperature was set to 69 degrees and the Central unit would occasionally come on and run for about an hour before cutting off. Temperature would not change, but evidently the Central unit produced some heat or it wouldn't have cut off.
I might add that for a home this size, I am surprised that the two unvented gas log sets are able to keep the home at 69 degrees.
I have been told that the efficiency of a HP decreases considerably when outside temperature is below 40 degrees, so when temperature gets to mid 30s, I use the gas logs.
Yes I have CO2 detectors and know the bad things about using unvented gas heat.

There are two types of heat pumps-air source and ground source (like paul and another mentioned). Ground source is the only heat source for a house, while air source usually needs a backup, depending where you live.

We installed an air source several years ago- it"s good to about 15 degrees. Beyond that, it kicks in for a few seconds, then shuts down and the LP furnace takes over.

I can not tell you how a heat pump does it but I can say it does. That is what I heat with and even when it was below zero the other day is was doing just fine keeping my house warm. I have never had to use the E heat on it by the way

(quoted from post at 19:21:23 01/08/14) I can not tell you how a heat pump does it but I can say it does. That is what I heat with and even when it was below zero the other day is was doing just fine keeping my house warm. I have never had to use the E heat on it by the way

Click to expand...

Yes--but it is my understand that there is a difference in Emergency Heat and auxiliary Heat.
I think most HP use auxiliary heat, when needed, but the emergency heat is a back up if a problem occurs with HP.
Please correct me if wrong.

On my unit it has normal heat which is the heat pump then you have the E heat which you have to switch on at the thermostat by hand. So at least on what I have you only have those 2 options and of course A/C

Have used heat pumps for many years, and you're right- auxiliary and emergency heat are two different things. And auxiliary heat will be needed anytime you get below freezing, at least intermittently. We've been into the low teens, and aux. has always handled it. But its not a true test, because when it gets that cold, we run the woodstove night and day.

I'm not sure, but I'm thinking the actual heat strips used are the same for aux and emer heat- but emergency just switches them on directly, bypassing the control system, if the system goes south. Maybe it adds some additional ones in emergency mode.

If the system is 12 years old, its probably on borrowed time at this point.

I can't tell you how a heat pump--air to air--works. But a geothermal system works by compressing the air after transfer the heat from the underground/underwater liquid. The compression is what raises the air temp to something over 100 degrees. That get blown through the house.
BTW If you use a well system or underground loop system the cost of a geothermal system should be the cost of a conventional forced air system plus the cost of the wells or the cost of the loops. I had to argue with the heating company but they finally saw my point. My wells were $2000 each and that's exactly how it worked out.

Lets leave geo thermal out of this and talk air-source heat pump only.
As you said there is a difference in auxiliary heat and emergency heat even though they both use the same heating strips.

In auxiliary heat mode the compressor comes on and tries to heat the home. Threw things like setback thermostats; target time settings; indoor temp drops settings; and even optional outdoor temperature sensors the heat pump decides if it needs auxiliary backup to help it heat the home. If it does the auxiliary heat will kick in; the heat strips will come on and help the heat pump recover.
My heat pump is set for a 2 degree indoor temperature drop. If I have the thermostat set on 70. The heat pump compressor comes on to try and hold 70. If the thermostat ever reads 68 (2 degree difference) the auxiliary heat kicks in the help.
If I raise the thermostat from 70 to 72 to warm the house up the thermostat still reads this 2 degree difference and turns on the auxiliary heat strips.
Same thing with the target time. If the heat pump is running; not losing ground; but not gaining ground; it would just run and run so the auxiliary heat kicks in.
This all happens automatically with the thermostat and circuit board in the indoor unit.
My unit also changes the fan speed to compensate for some of this.

Now in emergency mode things work a little different. You control this with your thermostat.
This mode is used if your compressor is broken (Freon leak; compressor shorted out); the outside unit is iced over due to a snow drift or other weather conditions that prevent you from using your heat pump. Hence the word emergency.
By switching to emergency mode you are basically turning off the heat pump and using your heating strips as a electric heater.
If I switch my unit to emergency it locks out the outside unit and prevents the compressor from coming on. The heat strips come on; and the inside fan blows giving me a heat source till I can get it fixed.
Now if only they could invent a emergency A/C mode I would be set.

My heat pump works great but then again we very seldom see water pipe freezing temperatures.

VADAVE, I've never heard of any heating system that compresses air to produce heat. I"ve had a geothermal system for 17 years, and it has nothing to do with compressing air. They are simply air conditioners, using Freon, but instead of using 90 degree air to cool the condenser in the summer, and 0 degree air to warm it in the winter, it uses 55 degree water from a ground source to heat or cool the Freon in the condenser. This makes it much more efficient than a conventional air conditioner or heat pump. The system pumps Freon the normal direction to cool, and reverses the direction in the winter. Mine has a propane backup, but if the heat pump is running properly, propane is never needed. Mine intentionally has no electric heat strips, as they are very expensive to operate.

Heat pumps use air for heat supply. Goethermal uses the water loop system like they would install in Minn.

Gary

I guess my main purpose for this post is to try and determine at what ambient temperature the auxiliary heating comes into play?
I guess the best way to determine this is to experiment with the heating elements activated.
On the Trane heat pump, at one of my homes this is how it worked:
Thermostat set at 70 degrees, turn setting up to 72 and if the thermostat was not satisfied in a unit determined time, one heat strip would cut on. If thermostat was still not satisfied in a determined time, second strip would turn on.
At thermostat there were three lights--one light--one strip, two lights-- two strips.
Now I could turn the thermostat to highest setting and three lights would flash and a separate light would flash indicating Emergency heat.
My present unit thermostat doesn't have these lights, so I will have to use my amp meter.

The experts say to just leave the thermostat setting at a constant temperature UNLESS you have a digital one that can "think". The reason- if you manually turn it down at night, then turn it up in the morning, the temperature differential will make the strip heaters work until it gets up to temp, thereby nullifying any savings from turning it down (and mama complaining about how cold it is).

With a digital thermostat, if you set it to be 65 at night and up to 72 by 8 AM, it will start the heating up process an hour or so ahead of the appointed time, so it has time to heat it up using only the heat pump and not the strip heaters.

The answer is "it depends on how effecient the compressor is" when aux heat strips are needed. My R22 compressor is good to about 35F but it wasn't desighned to be as effecient as they are today. Added to that it has lost some effecienc because of wear and tear. My R410a (Puron is a brand off 410) compressor does well at 15F which is about cold as it gets in Tx so I'm uncertain about anything lower.
At the risk of going too far and over simplifying,here are a few facts about the subject that explains how the system works.
Heat is present down to 0 Kelvin which converts to -459.67F. R22 sitting an open bucket can be carried like water at -40F. At -42F it will start to boil same as water does at 212F. It requires heat to boil anything so it is absorbing heat as it boils. Put R22 under 37psi and boiling doesnt happen until 37F. 76psi=45F boil.
R410a boils at -61 at sea level,15F @ 70psi, 45F@130psi. Just for grins,R503 boils @-126F.
To move heat from point A to point B,you need only minipulate the pressure on it and that's exactly what a compressor does. Raise the pressure and freon gives off heat,lower the pressure and it boils. During summer the compressor puts 300psi in the outdoor coil and freon heats the coil because it is giving up heat. When the same freon hits indoor coil at 60psi is boils by sucking heat from indoor coil. In winter,valves open/close to switch places with in and out coils. Round and round it go's.
I hope that answers you question without boring you or cause insomna trying to make sense of it.

(quoted from post at 00:00:37 01/09/14) The answer is "it depends on how effecient the compressor is" when aux heat strips are needed. My R22 compressor is good to about 35F but it wasn't desighned to be as effecient as they are today. Added to that it has lost some effecienc because of wear and tear. My R410a (Puron is a brand off 410) compressor does well at 15F which is about cold as it gets in Tx so I'm uncertain about anything lower.
At the risk of going too far and over simplifying,here are a few facts about the subject that explains how the system works.
Heat is present down to 0 Kelvin which converts to -459.67F. R22 sitting an open bucket can be carried like water at -40F. At -42F it will start to boil same as water does at 212F. It requires heat to boil anything so it is absorbing heat as it boils. Put R22 under 37psi and boiling doesnt happen until 37F. 76psi=45F boil.
R410a boils at -61 at sea level,15F @ 70psi, 45F@130psi. Just for grins,R503 boils @-126F.
To move heat from point A to point B,you need only minipulate the pressure on it and that's exactly what a compressor does. Raise the pressure and freon gives off heat,lower the pressure and it boils. During summer the compressor puts 300psi in the outdoor coil and freon heats the coil because it is giving up heat. When the same freon hits indoor coil at 60psi is boils by sucking heat from indoor coil. In winter,valves open/close to switch places with in and out coils. Round and round it go's.
I hope that answers you question without boring you or cause insomna trying to make sense of it.

Click to expand...

THANKS--very informative and (somewhat) easy to understand. Thanks for taking the time!

John in La had a good answer and he was dead on. This is a pic of my thermostat. The newer ones are electronic but still do the same thing. It has 2 little vials of mercury. The top one turns on the heat pump while the bottom one is 2 degrees behind the top one and turns on the strip heat (electric heat coils in the air handler). I leave the cover off the thermostat and can watch it tip over and the heatpump turn on etc. If it can't keep up finally the second vial tips and the strip heat comes on. No time involved in mine. It's worth noting that if the heatpump can't keep up it runs all the time with the strip heat cycling keeping the inside temp 2 degrees below the thermostat's set point. In the picture you can see in the top vial the mercury has tipped to the right side turning the heat pump on. In the bottom vial the mercury hasn't yet tipped over to turn the strip heat on.

I've been impressed with the sub 10 degree weather the past two nights as it ran most of the time but it never quite got 2 degrees below my setting of 66.

John's explanation of emergency heat is dead on too.

Don't want to muddy the waters but I was just reading somewhere where some folks have disabled their strip heat with a separate breaker or some other way. That might not be a good idea. Although not controlled by the thermostat the heat strips are turned on when the heatpump goes into defrost mode. In defrost mode the heat pump is switched to air conditioner mode even though it's set to heat. In ac mode it begins to take the heat from the air in the house and heat those outside coils to melt the ice off of them. It turns off the outside fan during this so no air is being pulled over them and they heat fast. In doing this the inside coils are getting cold--ac is on--thus to prevent cold air blowing into the house it turns on the strip heat to counter act the cold coils. If you somehow disconnect the strip heat then you will experience really cold air blowing into the house when the unit is defrosting.

It is 23 F outside here now my heat pump is off and the thermostat is on 72. In the 30's and raining is what gets it. just turns into a ice cube. It will reverse and melt it off. But just ice's up again. I don't have a wire to the strips. Have LP backup.

Chris Jones--I really appreciate your addition.
I understand what you are saying about "defrost" but I have never experienced cold air being displaced through the ductwork.
The owner stated that he had never turned the strips on, and it over 12 years old with no repairs, only serviced regularly.

Systems vary--who knows. I'd thought of pulling the wires from those strip heating elements on mine to ensure they didn't come on. Then I remembered the defrosting and decided to leave it connected. I have noticed on mine that when it's defrosting the air from the vents is extra warm so they must be on.