Residential Heat Pump

[mikem201]

Hello,

If you wanted to add a heat pump can you add one to your existing a/c unit or do you have to buy a whole new all in one unit? Also, on my furnace evaporator coil there are the two obvious vapor and liquid lines entering the evaporator but I noticed an extra connection for another line. Would that be for a heat pump?

[pacnw]

need new outdoor unit and possibly new indoor coil.

connection is NOT for add on of heat pump.

[mikem201]

need new outdoor unit and possibly new indoor coil.

connection is NOT for add on of heat pump.

why would I new evap coil. I know in heat pumps the evap coil and condensor are reversed but don't they just reverse the refrigerant flow to absord heat from outside and extract inside?

[chaard]

Indoor coil may not be large enough to handle the extra capacity in heat mode.

[junkhound]

What pacnw said.

HP function requires reversing valve (or setup to NOT have any AC capability), different controls, etc. Indoor coil for HP is typically 20% or more larger than AC only, unless you have an old 8 SEER POJ.

You will likely save money in the long run with a new high HSFP rated unit if you want heat from your vapor cycle equipment.

[Trehak01]

Correct me if I am wrong but, I believe you would also need a bi flow metering device for both indoor and out coils.

[mikem201]

Indoor coil may not be large enough to handle the extra capacity in heat mode.

So for the reversing valve instead of hot vapor running from compressor to condensor in AC mode. In heat pump mode it would start at compressor then to evaporator coil, on the outside unit absorbing heat from the ground or air then there is a metering device before arriving at the indoor condensor where the heat is then extracted over the coils where the cool return air is absorbing that heat when blowing over the coils, correct? There is no heat exchanger in heat pump mode, correct?

[jtrammel]

So for the reversing valve instead of hot vapor running from compressor to condensor in AC mode. In heat pump mode it would start at compressor then to evaporator coil, on the outside unit absorbing heat from the ground or air then there is a metering device before arriving at the indoor condensor where the heat is then extracted over the coils where the cool return air is absorbing that heat when blowing over the coils, correct? There is no heat exchanger in heat pump mode, correct?

I think you need to go back to heat pumps 101, research, then try again because ^^^ that makes no sense to an HVAC tech.

[mikem201]

I think you need to go back to heat pumps 101, research, then try again because ^^^ that makes no sense to an HVAC tech.

Im just starting out in HVAC in school so that is why. Can you tell me what part I got wrong?

[54regcab]

Correct me if I am wrong but, I believe you would also need a bi flow metering device for both indoor and out coils.

The outdoor unit already being a heat pump should have a bi flow device already installed.

[Snapperhead]

So when the reversing valve switches to heat , hot vapor goes from compressor towards indoor coil, the heat is then extracted from the indoor coils as the hot vapor runs through the coils, and Air passes over them. The gas then turns into liquid as it exits coil because the heat has been taken out. This now warm liquid travels towards the outside unit , passes though a metering device , causing it to turn into vapor again ,absorbing more heat from the outdoor air as it passes through coils, then vapor is sucked into the compressor , then discharged as a really hot gas back through the maze again. I fixed it for you ....


There is no heat exchanger in heat pump mode, correct? Those are used in refrigeration , not in your average central home air conditioners . Refrigeration is generally termed as anything used to keep food / beverage cold. You might find heat exchangers in many of those units.

A heat exchanger will have the liquid line and vapor line running tight beside each other ( this is Very lamens terms ) and one sucks the heat from the other

[mikem201]

I fixed it for you ....

Those are used in refrigeration , not in your average central home air conditioners . Refrigeration is generally termed as anything used to keep food / beverage cold. You might find heat exchangers in many of those units.

A heat exchanger will have the liquid line and vapor line running tight beside each other ( this is Very lamens terms ) and one sucks the heat from the other

In a gas furnace the evaporator coils are not the actual heat exchanger, correct? I have an upflow furnace and the evaporator coil is above the heat exchanger is what I am seeing I believe.

[mikem201]

The metering device is a regrigerant control device that maintains temp and pressure as it flows between condensor and evaporator, correct?

[chaard]

I'm gonna put my :.02: in here. These are my thoughts and not the industry norm. So take it with a grain of salt.

The indoor coil technically is a hx. The definition of exchange is to give and receive. The air over the
indoor coil in cooling is giving. The refrigerant in the coil is receiving the heat. The refrigerant in turn is giving back a cold coil and exchanging the warm air for cold air.

In hp mode the cool air over the warm coil is giving to the the refrigerant inside, and the refrigerant is receiving the cool air, the refrigerant in turn is exchanging the cool air for warm air.

The term heat exchanger in a 80% furnace is not a true heat exchanger. Because the hx is not receiving anything from the cool air over it. It is only giving heat to the air and warming it. The flue gasses are not absorbing the cool air cause its not condensing or changing the state of the heat or flue gasses in the HX.

Now on a hi eff. furnace the secondary coil which is actually first in the air stream is a true hx cause the warm coil is giving heat. The flue gasses are receiving the cool air and are condensing. So there is an exchange of heat before the warm air passes over the primary heat exchanger.
Again these are not terms normally used in our industry interchangeably. Just trying to help you understand how things work.
Let the flaming begin.

[mikem201]

I fixed it for you ....

Those are used in refrigeration , not in your average central home air conditioners . Refrigeration is generally termed as anything used to keep food / beverage cold. You might find heat exchangers in many of those units.

A heat exchanger will have the liquid line and vapor line running tight beside each other ( this is Very lamens terms ) and one sucks the heat from the other

Do you think based on this being my second semester in HVAC that my knowledge and description is pretty good?

[mason]

Do you think based on this being my second semester in HVAC that my knowledge and description is pretty good?

For now just know that you don't know enough.

Spend the next five years operating with an unquenchable thirst for knowledge and experience, take every job you are asked to do, within reason, like your next paycheck depends on it being accomplished the best way possible, if you're asked to change filters you be the best filter changer ever(remember what the components are from your books and remember where they are located on various units while you're at it), once you start installing/servicing units know that you have a huge amount of info and experience to get under your belt, stay humble and appreciative that you have a job, know that there is something to learn from everyone, even if it's what not to do. If you do this ^ and become a member of this site and are willing to take the lickings for doing things wrong and getting schooled by the more experienced members here without acting like a baby, and you have some natural abilities related towards this occupation you will turn out better than at least 80% of the folks who get into this business.

[garyed]

The way I explain heat pumps is to think of how a window AC unit blows out cold air inside & hot air outside. If you could just turn it around in the winter & let the hot air blow inside & the cold air blow outside that is what a heat pump does. It just takes some extra controls & valves to do it.

[54regcab]

The way I explain heat pumps is to think of how a window AC unit blows out cold air inside & hot air outside. If you could just turn it around in the winter & let the hot air blow inside & the cold air blow outside that is what a heat pump does. It just takes some extra controls & valves to do it.

I use this explanation also, easy for new guys and customers alike to understand.

[Snapperhead]

In a gas furnace the evaporator coils are not the actual heat exchanger, correct? I have an upflow furnace and the evaporator coil is above the heat exchanger is what I am seeing I believe. OH ! So THATS the heat exchanger you were referring about , in a FURNACE ... You had me confused because you were talking about Heatpumps and the refrigerant cycle and something about an exchanger. There are heat exchangers in refrigeration units and I thought thats what you were speaking about.

So yes , you are right , if you have a gas furnace as "back-up heat" in addition to a heatpump in your scenereo above, then yes , a FURNACE has a HX ( heat exchanger )

Sorry for the confusion , but our friend Chaard above explains it as well.

But just so you know , having the correct terms helps alot.

For example , (technically ) Heatpumps have indoor and outdoor units , you dont call them evaporators and condensers , because once you run it in Heat, the indoor unit is suddenly the condenser. Make sense ?

In straight AC , yes the outdoor is a condenser , indoor is a evap , always

In refrigeration , like a walkin cooler , outdoor is condenser , indoor evap

In refrigeration you have heat exchangers , but you will have to get your teacher to show you one.

In furnaces you have heat exchangers

[toocoolforschool]

Correct me if I am wrong but, I believe you would also need a bi flow metering device for both indoor and out coils.
you are correct. So just have the dude install that for the cost of a new coil and air handler.

[ParamountAir]

Back to your original question - never add a condenser (ac or hp) to an unmatched coil (evap or fan coil). This system is supposed to serve someone well for 15-20 years, why would you want something that isn't factory tested for performance and if not matched probably not warrantied?

Don't get cheap on this customer, or you will be back to repair it for life:)

[hvacrmedic]

I'm gonna put my :.02: in here. These are my thoughts and not the industry norm. So take it with a grain of salt.

The indoor coil technically is a hx. The definition of exchange is to give and receive. The air over the
indoor coil in cooling is giving. The refrigerant in the coil is receiving the heat. The refrigerant in turn is giving back a cold coil and exchanging the warm air for cold air.

In hp mode the cool air over the warm coil is giving to the the refrigerant inside, and the refrigerant is receiving the cool air, the refrigerant in turn is exchanging the cool air for warm air.

The term heat exchanger in a 80% furnace is not a true heat exchanger. Because the hx is not receiving anything from the cool air over it. It is only giving heat to the air and warming it. The flue gasses are not absorbing the cool air cause its not condensing or changing the state of the heat or flue gasses in the HX.

Now on a hi eff. furnace the secondary coil which is actually first in the air stream is a true hx cause the warm coil is giving heat. The flue gasses are receiving the cool air and are condensing. So there is an exchange of heat before the warm air passes over the primary heat exchanger.
Again these are not terms normally used in our industry interchangeably. Just trying to help you understand how things work.
Let the flaming begin.

Yes, you're correct....those thoughts aren't the industry norm. I'd say that your definition of heat exchanger is different than pretty much every textbook definition. ;)

[chaard]

Yes, you're correct..
That's all that matters. ;)