Central Air Just went out

[xsn10s]

Have you noticed a light on your thermostat that says aux heat? The heat pump that they install here (Gulf Coast of TX) has electric heat installed at the exchanger.

The operation of a heat pump is pretty simple:

1. A heat exchanger transfers heat from the hot refrigerant into the less-hot home.
2. The refrigerant is decompressed, which makes it very cold.
3. Another heat exchanger transfers heat into the cold refrigerant from the less-cold outdoor air.
4. Refrigerant is compressed, which makes it hot.
5. Start over again at #1 and repeat the cycle.

See number 4? Heat of compression depends on the discharge pressure of the compressor. The discharge pressure is dependent on the temperature of the condensed refrigerant. The temperature of the condensed refrigerant is dependent on the temperature of the air moving through the condenser (discharge cooler in an industrial setting). If it's cold outside the condensed liquid is cold and therefor the temperature is low. No heat to "pump" back into the house. So they turn on electric heat.

No I haven't seen that aux heat light. I just manually switch it to aux heat. When that happens the unit outside stops working and the furnace inside the house turns on. When I switch to aux heat there's a noticeable difference in my power bill.

 

[cohunt]

Have you noticed a light on your thermostat that says aux heat? The heat pump that they install here (Gulf Coast of TX) has electric heat installed at the exchanger.

The operation of a heat pump is pretty simple:

1. A heat exchanger transfers heat from the hot refrigerant into the less-hot home.
2. The refrigerant is decompressed, which makes it very cold.
3. Another heat exchanger transfers heat into the cold refrigerant from the less-cold outdoor air.
4. Refrigerant is compressed, which makes it hot.
5. Start over again at #1 and repeat the cycle.

See number 4? Heat of compression depends on the discharge pressure of the compressor. The discharge pressure is dependent on the temperature of the condensed refrigerant. The temperature of the condensed refrigerant is dependent on the temperature of the air moving through the condenser (discharge cooler in an industrial setting). If it's cold outside the condensed liquid is cold and therefor the temperature is low. No heat to "pump" back into the house. So they turn on electric heat.

I'm an hvac technician, a heat pump is just an air conditioner with a reversing valve--- it basically changes the inside evap coil into the outside condenser coil and Visa versa

Technically, unless you are certified you can't buy/install anything that has refrigerant in it (freon is a brand name, not a type)--- people will sell anything on line now though--, if you buy your own equipment my company hikes their labor rate by 1.5x and offers no warranty---- I know it's expensive but sometimes it's worth it to buck up and pay the price.

In my area, a/c parts are in high demand and some parts are on a 8-10 week back order from the supply house

Don't forget to pull permits so when you sell your house you don't run into issues

 

[Mike6158]

a heat pump is just an air conditioner with a reversing valve--- it basically changes the inside evap coil into the outside condenser coil and Visa versa

Exactly. Instead of removing the heat from the heat transfer fluid (refrigerant) the outside coil is supposed to pull heat from the outside air. If it's cold outside the heat source isn't a heat source.

I can walk into any hardware store that sells window unit air conditioners, that use a refrigerant, probably non CFC, buy it, take it home, put it in the window, plug it in, and turn it on. No certification required.

My refrigeration experience is industrial scale. Like each 6 throw 3 stage compressor is driven by a shade over 1,000 HP gas engine. We use propane (generally), pull the chiller low side down to 3psia and cool the 900 psig gas stream to -35 to -40 F. We also have centrifugal refrig compressors driven by solar turbines. The principals are the same. Physics is physics...

 

[cohunt]

Exactly. Instead of removing the heat from the heat transfer fluid (refrigerant) the outside coil is supposed to pull heat from the outside air. If it's cold outside the heat source isn't a heat source.

I can walk into any hardware store that sells window unit air conditioners, that use a refrigerant, probably non CFC, buy it, take it home, put it in the window, plug it in, and turn it on. No certification required.

My refrigeration experience is industrial scale. Like each 6 throw 3 stage compressor is driven by a shade over 1,000 HP gas engine. We use propane (generally), pull the chiller low side down to 3psia and cool the 900 psig gas stream to -35 to -40 F. We also have centrifugal refrig compressors driven by solar turbines. The principals are the same. Physics is physics...

There are heat pumps that now work down in the -15° vicinity , but youll pay a premium price for them--- Window units are "sealed units" just like refrigerators and freezers and ptacs, etc that dont require certifications-- it's when you get into condensers/coils/mini splits etc that it requires a certification ---- but like I said--- legal or not, you can buy anything online nowadays--- technically you can't buy refrigerant unless you have a 608 or better, but I see it online every day---, also depends on your jurisdiction for what is required, but 608/609 is a federal/epa law

 

[Mike6158]

Makes sense. I'd rather hire a tech for the big stuff so no problem there.

 

[Coyote Shadow Tracker]

We had a really good Heat Pump when we first moved into a new home. As the thread i started several years ago was for the new COST of a new TRANE Unit. The newer Heat Pumps in the South work really well and efficient for $$$$. It all depends on the size of your home and the unit to match along with SEER of the Heat Pump Unit.
The questions about "Emergency Heat".
Our unit is -was the top of the line Train Heat Pump. Everything is controlled by computer and Blue Tooth (also hard wired). We have a unit on the wall to control the inside Temp and can also control by our phones. When the outside air temp get below what the system can draw heat it will go into and extra heat system which is Electric HEAT inside the Air Handling unit. Now we have lived with Heat Pumps for 27 years and rarely has the extra HEAT Strips ever came on. Our new unit will run a real long time trying to keep the heat up to the temp you want. It is best to keep the Thermostat at the same setting all the time so there is not a big swing in the unit to provide the heat you want. Example you set your Thermostat at 68 when going to bed and then having it go to 74 when you wake up. This works good with Natural Gas or Oil Heat, but not with a Heat Pump. The Heat Pump recognizes the 6 degrees difference and tries to get to it. The computer in the system then switches to Heat Strips to get the heat up in a few minutes. Best to not have a big swing.
Our home is total electric and the Trane is very efficient and cost reduction. Yes there will be more electric used with the Heat Strips, but if you use your Heat Pump correctly you save a lot of money.

 

[Mike6158]

I had state of the art Trane units but the "state of the art" time frame is probably at least 15 years ago, maybe 20.

That's a real good point about not letting the thermostat swing the temperature. If I remember right the heat strips start to come on here when the ambient air temp outside is 45-50 degrees. When it's 20 degrees outside (I'm only 90 miles inland from the Gulf Coast of Texas, west of Houston but we've had 20's in the winter), the unit ran continuously, with the aux heat strips on, unless I supplemented with propane or electric heat. The house is older and not insulated as good as it could be. The windows are dual pane, aluminum, contractor grade windows.

I had metal frame windows when I lived in Greeley, CO. During the first segment of the remodel I switched them out to wood frame, dual pane, windows. That made a big difference. Wood is an insulator, metal is a conductor. The old metal windows would form ice on the inside when we had 0 degree days.

I don't mind hot weather. Earlier today I drove 90 miles to visit my youngest daughter and her family. I wondered what the change to my fuel mileage would be if I turned the AC off. It was 98 - 99 degrees outside. I drove down and back, windows down, sliding back window open, AC off. It wasn't pleasant but it wasn't horrible. Fuel mileage improved by 2.5mpg over the 180 mile round trip. Not bad. For the record, it wasn't bad but the AC will be on when I drive to the range tomorrow. It's a good/better/best thing.

 

[cohunt]

Manual J, manual S, manual D

Gotta do the calcs and math to size the unit correctly--- otherwise your just pulling a number out of your petunia

Newer Higher efficiency systems often have lower delta T numbers but higher cfm/airflow --- your duct system has to be able to handle the airflow too.

Any monkey can slap a system in, but it takes some knowledge/charts/software to design a system correctly

 

[cohunt]

I had state of the art Trane units but the "state of the art" time frame is probably at least 15 years ago, maybe 20.

That's a real good point about not letting the thermostat swing the temperature. If I remember right the heat strips start to come on here when the ambient air temp outside is 45-50 degrees. When it's 20 degrees outside (I'm only 90 miles inland from the Gulf Coast of Texas, west of Houston but we've had 20's in the winter), the unit ran continuously, with the aux heat strips on, unless I supplemented with propane or electric heat. The house is older and not insulated as good as it could be. The windows are dual pane, aluminum, contractor grade windows.

I had metal frame windows when I lived in Greeley, CO. During the first segment of the remodel I switched them out to wood frame, dual pane, windows. That made a big difference. Wood is an insulator, metal is a conductor. The old metal windows would form ice on the inside when we had 0 degree days.

I don't mind hot weather. Earlier today I drove 90 miles to visit my youngest daughter and her family. I wondered what the change to my fuel mileage would be if I turned the AC off. It was 98 - 99 degrees outside. I drove down and back, windows down, sliding back window open, AC off. It wasn't pleasant but it wasn't horrible. Fuel mileage improved by 2.5mpg over the 180 mile round trip. Not bad. For the record, it wasn't bad but the AC will be on when I drive to the range tomorrow. It's a good/better/best thing.

Sometimes keeping the windows up and a/c on can save gas---- aerodynamics of the car come into play and often times windows up will give far better mpg even with a/c on

 

[xsn10s]

Mine is a Goodwin circa 2006. So it's an older unit. But I've been pretty happy with it's function during the summer in 105 degree temps and cold Oregon winters. I compare our energy costs with my friends who have AC and gas furnaces. We actually pay less than they do. I keep kerosene heaters for backup heating.

 

[HockeyDad]

Just wish that it wasn't in the 90s until we get a new one.

103 at 9:00 pm here.

 

[Mike6158]

Sometimes keeping the windows up and a/c on can save gas---- aerodynamics of the car come into play and often times windows up will give far better mpg even with a/c on

I tend to be analytical. Some would say too analytical. I think I agree but I'm going to have to think about that a little more

I've had my pickup a shade over a month. I got it with 4 miles on it (because nobody else is dumb enough to buy a new pickup in this economy). At this moment it has 10,029 miles according to my GMC app. I drive more than a lot of people.

I've checked the mileage with the windows up and the AC on precisely 1.2 sh**ton's of times.

The baseline is established. I am not going to establish an equivalent 10,000 mile baseline for windows down and AC off until fall or winter, if ever.

But I reckon what I established yesterday is close enough.

15mpg = 0.067 gallons per mile = 6.7 gallons per 100 miles

13mpg = 0.077 gallons per mile = 7.7 gallons per 100 miles

@ 3.00 a gallon, in 10,000 miles = 670 gallons = $2,010.00 with the AC on

@ 3.00 a gallon, in 10,000 miles = 770 gallons = $2,310.00

Theoretical savings with the AC off, is probably negative because prolonged exposure to 99 degrees and 72% humidity will probably result in a hospital stay.

PS - my electric bill averages $120 or less a month all year and I don't run my heat pumps anymore.

 

[Coyote Shadow Tracker]

Goodwin are GREAT. May have 0ne instead of a TRANE if it was available. Supply was so short when ours went out we were lucky to get it. They ran out of units and just one in the size we needed.

 

[Mark37082]

The HVAC companies are very busy right now. My daughter and nephew both had their AC units bite the dust in the last 2 weeks. I had to replace one full unit and a condenser on another last year. All I know is we have become so dependent on living in perfect temps in our homes. Living in an area where there are extremes from cold to hot during the year put a priority on good HVAC and strain on the bank accounts. I prefer cold vs hot.