Heat Pumps
Air to Air
What are they ?
Is a heat pump really cheaper to operate ?

Winter                 
Heat Pumps are air conditioners but when they produce heat the gas / refrigerant reverses it's flow and then it's called a heatpump.

When your heatpump thermostat wants heating during the winter time the flow of refrigerant is reversed and the outside coil becomes the "cold" evaporator coil and the indoor coil becomes the "hot" condenser coil. The heat is absorbed by this gas / refrigerant via the air crossing the outdoor coil then moved by copper pipes to the indoor coil and air crosses this coil absorbs the heat and is blown into the conditioned space, your home.

The component part or valve that reverses this refrigerant flow is called the reversing valve.  There are 3 components that are primarily responsible for the flow of refrigerant or gas. They are the compressor, the evapator coil (inside) and the condensor coil (outside) and they are connected by the copper pipes which will carry the gas / refrigerant to each of these 3 components.
By the way that gas should never leak out and I mean never.  If it does then there is a leak somewhere.

Don't try to convert the air conditioner to a "Heatpump". It requires some engineering re-design and won't work. Believe me that has been tried thru the years but is not successful. Leave it to the people who know what to do "The Manufactures".

As a home owner what you are really interested in is your comfort be it heating or cooling NOT the nuts and bolts. Be comfortable and have your contractor guarantee your comfort at the best economical cost of installation and monthly bill of operation.

                                 How does it do that ?
During summer months the unit will pick up heat from the interior conditioned air by using an air-cooled
evaporator coil and discharge this heat into the outside air through a forced air condenser.


So What is a Heat Pump ?

Since the 60's this question has been asked a lot so you are certainly not by yourself.

 The Heat Pump provides heating & cooling and heating is provided at a very economical rate. Heat Pumps are good & economical even in
 cold climates.
 Heat pumps are a very good source for heating and very economical as well. The biggest draw backs are they may not be properly installed and the most common complaint is the air coming out your registers is not as hot as your furnace, thus you very well may complain of being too cold. Technically the heat pumps air may be around 95 degrees but the furnace air is around 125 degrees. Which air is hotter?
If your accustomed to the "Hot Air" of the furnace then you may not be satisfied with a heat pump. With furnace heating that's why a humidifier, (mist spray of water), is used. Without the humidifier the air is very dry and may cause items to dry. Once on Sanibel Island on the west coast of Florida the home became so dry the tongue & groove wall started to come apart due to the dryness.

The below should help in you decision of a heat pump. If you have a question please send me an email via this site and I will get back.

Some terminology you might run into, "Air to Air".

Air to air simply means air goes across the outside condenser coil to absorb heat or get rid of heat depending on the mode it is in and the air across the evaporator coil, the indoor unit,  picks up heat or cooling, (removing heat from the air or adding heat ),  to distribute to your conditioned rooms so you may be comfortable. A water to air means the condenser coil uses water to do the same thing, (that may be a water cooled unit or Geothermal unit), & the indoor evaporator uses air to distribute heat or cooling as mentioned before.
 
Click on item or read by paging down

For a heat pump to properly be presented to the home owner the following items should be included in the presentation:

1. A load calculation showing the BTU requirement, (room by room or whole house), for the customers comfort. .
2. A manufactures specification sheet showing the heat pumps BTU output at different outside temperatures.
3. The heat pump balance chart that shows the heat pump will produce enough heat down to a given temperature. Colder than the balance point, (where the load calculation & the heat pumps production lines cross), will require supplemental heat to assist the heat pump or another form of fuel will take over at those colder temperatures.

Supplemental heat and auxiliary heat should also be explained.
Supplemental heat is needed for those temperatures below the balance chart where the heat pump can no longer produce enough heat for comfort to be maintained and auxiliary is less than the heat pumps output and comes on when the system is not working and needs a serviceman. Auxiliarys intent is to supply some heat until the system can be repaired.

How a system uses supplemental heat, what type, and how much is diverse as their are dealers / contractors. The guiding factor should be the operating cost & that can be given by the dealer / contractor. The balance chart helps as well.

Remember your comfort must be maintained at design temperatures & the contractor should guarantee it. Don't get hung up in the nuts & bolts.

Example of a computerized Design Temperatures for Cedar Rapids, Iowa
Each location will have a "Design Temperature" either in Manual "J" or a computerized data that is in accordance to Manual "J" .
Shown below is a computerized calculation form in accordance with Manual "J"
Notice for this location a summer 88° outside with 75° inside,  winter -5° outside and 70° inside.

Heating & cooling BTU's calculated will take design temperatures into account.


Weather Data Hours per year for Des Moine, Iowa ( This is also located in Manual "J" )

All dealers / contactors have or should have this information after all it's part of their job.

To see how long the Heat Pump does it's job one needs to look at the Heat Pump balance chart which should be done by the contractor quoting or doing the job.  That tells you the Heat Pump will perform down to a given temperature. Temperatures below the balance point one needs supplemental or make up heat it in the form of gas, electric, oil & so on and according to your location and local rates for fuel. ( The annual btu requirement information can be found in the dealers Manual "J". )

What is the cost for the supplemental fuel ?
You should be shown the projected annual total amount of btu's required, ( in the dealers manual "J"),  to see what fuel would be the better choice with a good payback, ( I like 5 years or less ). Also the hours per year in 5 degree increments of your location, an example of average hours per year , click this and as shown below.

Usually the heat pump unit is controlled by "outdoor thermostats" which turn the heat pump off at a set outdoor temperature and starts the supplemental heat. There are various ways for this control and should be discussed with the contractor.
Remember it's your comfort we are concerned with not just the nuts and bolts.

In air conditioning you will notice that the OUTSIDE unit gets hot while the indoor coil gets cold. The "Heat Pump" reverses this process.The OUTSIDE unit now blows cold air during it's winter season and the inside coil gets hot.
Through it's own process it takes HEAT from the outside air and blows it into your home via the gas or refrigerant cycle. There is plenty of heat in the cold air outside air even though you think it's cold. That is what a heat pump does is take outside air heat & puts it into your home.

However the colder it gets outside the less "Heat" the heat pump puts out yet your home requires more heat to keep you warm, (from Manual "J" calculation Heat Loss).  The Heat Pump Balance chart will show the heat pump will heat your home until it reaches a certain temperature as shown on the balance chart. Usually the Heat Pump will do it's job down to somewhere around 32 - 40 degrees then other types of heating are needed to make up the increase of heating BTU's as it gets colder.  Below where the two lines cross on the balance chart means the heat pump will not due the heating and the colder it gets the more the heat pump will not keep up with cold temperatures.  Say for example at 38 degrees 70,000 BTU's of heat is needed to maintain your comfort and the heat pump only delivers 36,000 BTU's.  Not enough heatpump heat unless you have planned & installed some other supplemental type.

Some use electric heat for supplementary heat others use gas, oil, and other types of heat at those colder temperatures. That will depend on your area and it's cost for fuel. The following sample balance chart will help explain further.

Auxiliary heat is mainly for some heating if the heat pumps compressor goes out or there is a mal-function with the heat pump unit, until it's repaired.

The heating difference must come from somewhere, (gas, electric, oil, etc), if your comfort is to be realized. That's one of the reasons that a "Load sizing calculation" and a "Heat Pump Balance Chart" should be done.

 
The "Heat Pump" heating efficiency is rated as C.O.P., (Coefficient of performance). That simply means wattage converted to Btu's. The amount of unit Btu's divided by (wattage x 3.41btu's).

Another heat rating is called the "HSPF", the Annual Heating Season Performance Factor.  A unit's heating HSPF is listed in the "ARI" Directory. The HSPF number can be used to estimate the annual heating energy consumed by the heat pump. Including the indoor & outdoor fan motors, the crank case heater, & the controls.

The air conditioner part of the system is rated as SEER. The larger the seer the more btu's per electrical comsumption. (Ex: 12 SEER is btu's per watt of electricity that runs the machine.)

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One needs to be aware of the rise in air temperature in a furnace and a heat pump.
Especially when replacing a furnace with the heat pump. This should be explained to the home owner before hand.
A furnace may be around 125 degrees in it's air temperature to a room while the heat pump may be 95 degrees. Both are warm or hot and will keep your comfort but the heat pumps air seems to be colder to the hand when a customer checks the feel of the air blowing out of the grille. Comfort will still be there but customers need to be aware of the difference. Either one needs to be properly installed and especially the heat pump with the balance chart

The heating temperature of the heat pumps air is not as hot as the gas furnace therefore some people may complain at first. The heat pumps air is in the 90°'s but for very cold climates the MOST efficient form of heating is only good to the application rating of approximately 38° to 40°,  after that another more economical fuel, (usually a gas furnace), kicks in & the heat pump stops. The colder it gets outside the less heat the heat pump puts out. Sometimes that "Extra" heat is in the form of resistance or electrical heat which is the most costly fuel you can find.

 
Spec data sheets on a specific heat pump to show as an example !

Specification data is available from the dealer and shows good information for the proposed unit.

The below specs are examples of a 5 ton Heat Pump showing the rated cooling btu's & heating btu's at various outside temperatures.

Don't confuse this as only heat pumps have this type of info. No matter what the equipment there is a performance specification sheet on it.

Cooling:
Ex: Outdoor temperature of 95° and 67° entering wet bulb & at 80° dry bulb at 2000 cfm the Btu capacity would be 59,700 Btu's.  
That same unit at 115° outside would be 53,200 Btu's

Air conditioning specs on a 5 ton heat pump,  single or 3 phase unit

Heating data is as follows:

Notice the colder it gets outside the unit capacity is less. That's why a heat pump balance chart is done so you can see where the heat pump no longer does the job & other types of heating "KICK in" at colder temperatures
Heating specs on a 5 ton heat pump,  single or 3 phase unit


All heat pumps will have the below type of data from the manufactures specification sheet
They should have a rating by ARI laboratory of their production at Outside temperatures of 47° & 17°
This type of information is used to compile part of the balance chart.
"Heat specs on a 5 ton heat pump" (Always size the Heat Pump according to the Air Conditioning heat gain load calculations)

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The Heat Pump balance chart is also done with these facts. Below is an example of a Heat Pump balance chart. (For AC people it can be found in the Manual J book).

One takes the Heating load calculation & makes the 1st line by drawing from the residence Heat Load to a 65 degree temperature, ( 65 degrees is always used), from the spec sheet take the Heat Pump data & draw the 2nd line. You can then see where the Heat Pump does it's job to where the two lines cross. Below that line you need other heat to keep up with the colder temperatures and may very well not use the heat pump at these colder temperatures.

 Usually other more economical fuels take over then, ( depending on your area ).

 
The most economical fuels for heating are: (1). Heat pump, (2). Natural Gas, (3). Propane Gas, (4). Oil, & in last place is (5). Electrical heat, (aka wire resistance heat). I am not familiar with boilers or radiators.


The Heat Pump only satisfies your comfort to the "Balance" point ( where the two lines cross then straight down is the balance temperature - meaning the heat pump will do the comfort job down to that temperature ). Temperatures lower than the balance point require additional fuel for heating and is needed since the heat pump will not produce enough heat for your comfort and probably cut off if designed properly and let a more economical heat and fuel take over.
Every installation of a heat pump should have a balance chart for the customer & the installing contractor. Heat Pumps at and above the "Balance point are probably the most economical form of fuel you can get and that leads to the "Bin Method" for hours a year at given temperatures. Annual operation cost of the higher efficiency units be cooling or heating & the cost of their annual fuel usage or requirement will determine for you which is the best purchase. The AC & Heat Dealer should be able to provide this information.
 
If you have or getting a heatpump a heatpump balance chart should be required.


How to do a heat pump balance chart.
Forms & Examples are below


J-1 Heat Pump chart form & the above "How to do a chart"  ( to save or print, right click form , "print picture" or
"save picture as" then name it & save to the directory of your choice located on your harddrive ).


The Load Calculation Heat Loss shown as the Blue Line
If the Design Temperature for Winter is -5 deg Outside and 65 deg then below is the 1st step of the chart.

At 65 degrees outside 0 btu's required
at -5 degrees outside120,000 btu's are needed.



The Heat Pump Production from Manufactures Spec Sheet shown on the below chart.



The two charts put together

So 2 things are needed for a balance chart to be properly done:

1. A Load calculation of your home, (from the installing dealer or a source that is familiar with calculating loads, and unit sizing and factors in accordance with Manual "J".  It requires the home and it's complete envelope be measured, see "Unit sizing calculations" selection from the Menu)

2. Specifications on the heat pumps production at various temperatures. ( from the unit manufacturer but the dealer will have this data)

Have questions just send me an Email  clik here


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 More Heat Pump balance examples
as the outdoor temperature starts to drop so does the capacity of the Heat Pump system. On those colder days where the capacity drops below the required heat loss, (balance point), additional heat must be supplied. That heat can be electric, gas, or what you and the dealer may agree to.
The building heat loss is in red. Unit capacity in black. The point at which the unit capacity line & the calculated heat loss intersects is the balance point. This example has heat loss at 34,500 BTU/hr & unit capacity at 34,500 BTU/hr at 32.5 degrees
at 10 degrees the heat pump will require an additional 36,500 BTU/hr to maintain comfort. The heater selected must deliver at least 36,500 BTU/hr at the designed point and thats with the output of the "Heat Pump".
Emergency or Auxiliary Heat

In this example:
10 degrees is the full capacity required of 57,500 BTU/hr. and at 80% this would require an input of 46,000 BTU/hr. Usually this is electric heat and is to maintain some comfort until the compressor or unit is repaired.
In colder climate areas electric heat may make up the difference of heat needed
Emergency or Auxiliary heat requirement may vary from 60% to 100% of the heat required at design temperature conditions.
If you have any question please contact me.

Download or print a heatpump balance chart form (PDF)  click >   HeatPumpBalChart.pdf
 
Average hours per year at shown temperatures per location.
In the above take Raleigh, N.C. below the heat pumps ability (size) the heat pump will no longer take care of your comfort and other heat needs
to "kick" in to maintain your comfort below 35degrees. Approximately 682 hours per year. Less than 2% of the heating season.
 Not bad when the majority of the heating season can be handled by the heat pump.
The balance chart will tell how long the heat pump can maintain you comfort without auxiliary heat.
 
Heat Pumps should be sized according to the "Cooling" load calculation & in accordance with Manual "J". That is primarily due to maintaining latent or moisture control in the air conditioning season.  

Air conditioning for humid areas would be in trouble if a heat pump was sized according to the heating.
It has been brought to my attention that areas that have very little air conditioning may be sized according to a heating calculation but I still wonder for air conditioning do those areas have any humidity to deal with during the very little cooling season.  

I don't know of any manufacturer that say's to size according to the "Heat Load" regardless of your temperature and if there is please send an E-mail who that manufacturer may be.