Air Conditioner with Heat Pump

billbo

Member
Yes, normally a functioning heat pump reduces humidity just like the air conditioner. The LP furnace will increase humidity, just the nature of burning LP. I ran the HP this AM, temps were 48F and it was nice. Finally got motivated to bring in the cube heater though, much less noise.
 

TJLee089

2013 Itasca Reyo 25R
You are incorrect on both counts. Unlike an air conditioner, where a cool surface causes condensation and drainage of moisture, the heat pump does no such thing. It simply warms the air as air passes through the warm heat exchanger. (I've had heat pumps in homes since 1973.)

The LP furnace does not add any moisture to the air. The air simply passes through the warm heat exchanger, warming it. It is true than the combustion of LP produces water in the exhaust gases (along with carbon dioxide and traces of deadly carbon monoxide), however this gas is external to the inside of the coach. If it were not so, you would likely wake up dead, otherwise known as not waking up at all.

Yes, normally a functioning heat pump reduces humidity just like the air conditioner. The LP furnace will increase humidity, just the nature of burning LP. I ran the HP this AM, temps were 48F and it was nice. Finally got motivated to bring in the cube heater though, much less noise.
 

Hooligan2

Member
I have 15K AC/ HP., seldom use the heat pump. Not needed above 65 and not effective below 40 deg. AT 40 it usually runs longer than it rests and at 35 or so it runs continuously. At that point the thermostat switches to the propane heater. Cube heater quieter and in the 20's augments the propane heater keeping the bedroom temps more constant.
Ordered unit with Heat pump (+$525 option) would not replace the AC with HP option.
 

TJLee089

2013 Itasca Reyo 25R
On my rig, by design, if on heat pump and the temp is something like 2 degrees below the thermostat set point the gas furnace kicks on in addition to the heat pump. When temp within 1 degree of set point gas furnace shuts off. I sometimes use the furnace for a quick warm up in the morning (15 minutes or so) but that's about it.

I have 15K AC/ HP., seldom use the heat pump. Not needed above 65 and not effective below 40 deg. AT 40 it usually runs longer than it rests and at 35 or so it runs continuously. At that point the thermostat switches to the propane heater. Cube heater quieter and in the 20's augments the propane heater keeping the bedroom temps more constant.
Ordered unit with Heat pump (+$525 option) would not replace the AC with HP option.
 

billbo

Member
You are incorrect on both counts. Unlike an air conditioner, where a cool surface causes condensation and drainage of moisture, the heat pump does no such thing. It simply warms the air as air passes through the warm heat exchanger. (I've had heat pumps in homes since 1973.)

The LP furnace does not add any moisture to the air. The air simply passes through the warm heat exchanger, warming it. It is true than the combustion of LP produces water in the exhaust gases (along with carbon dioxide and traces of deadly carbon monoxide), however this gas is external to the inside of the coach. If it were not so, you would likely wake up dead, otherwise known as not waking up at all.

I am 100% CORRECT on both counts. Please read up a bit. Yes, normally we think heat pumps remove moisture in the room in cooling mode - just as you said. They also remove moisture from the heated space as the air circulates. That's why I installed a humidifier on every heat pump I've had in every home since 1972 when I bought my first home. The inside air of a house heated by a heat pump quickly becomes arid like the desert and that's a huge problem for me. I can certify in my humid environment of NW GA where humidity outside is frequently above 90%, winter or summer, the inside of the house will quickly fall below 30% humidity without the humidifier in the heat pump working. I check that regularly because of health condition. Right now I'll be glad to leave the "desert" of Denver. I left my portable humidifier at home so I boil water when we are in the RV in a steam pot at night to get the humidity up. If you had certain health conditions you most certainly would know these things. That's the only reason I have stayed in the Sunny South most of my life, the dry arid desert states are just unfriendly to my health. I did live in Washington St a long time on the western side, lots of humidity there too. Most folks who own a heat pump have a humidifier installed as well to regulate around 50% inside the home.

I also have LP at home for emergency heat after the blizzard of '93 left us with no power for three weeks. LP will definitely release moisture into the home. You should dehumidify running LP in extended modes. I do. If you do not dehumidify you will soon see moisture accumulate on the windows inside. I agree the combustion byproduct and a lot of heat is lost in the RV with the design of the LP furnace but it also introduces considerable moisture. The water is actually what causes a visible flame when LP is combusting. And...yes, in the RV most of it does go out and the vent and the heat exchanger does not accumulate it appreciably. It becomes a really big problem if you use an unvented heater like many do, gas logs for example and those wall heaters. If you use those the house will definitely get wet without a dehumidifier and you must open some windows or die.
 
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billbo

Member
Here's a note from a HVAC company:

How to Combat Low Home Humidity During Heating Season

To make life more comfortable, preserve your home and its contents and help your heating system perform optimally, you need to add moisture to the indoor air. One option is to use portable humidifiers in different rooms of your home, but it’s essential that the output of each unit matches the size of the room or you could add too much moisture.

The most efficient way to increase home humidity is with a whole-house humidifier. These units are installed in a home’s HVAC system and add just the right amount of moisture to the air that’s circulating through the ductwork. A trusted HVAC professional is your best source of advice and assistance with sizing, selection, and installation.
 

TJLee089

2013 Itasca Reyo 25R
100% WRONG on both counts.

The reason your house gets dry in the Winter is not because of the heat pump. It's because of the exchange of cooler air from the outside (e.g. bathroom fans, dryers, doors, windows opening) which holds much less absolute moisture than the inside air. Air at 35F, 100% relative humidity has a RH of 28% when heated to 70F. If you were correct, folks heating without heat pumps would not need humidifiers. They do. In fact, according to your logic folks heating their home with LP might need DE-humidifiers in Winter. They don't. I have a heat pump and a wood burning stove. My house gets dry not because of the heat pump, but because of the outside air (cooler with lower absolute humidity) brought in to support combustion. You offer no explanation as to HOW the heat pump could possibly remove moisture. You are misinterpreting you experience. If you carefully re-read my post, you will see why.

You are correct that an unvented LP source will add moisture, however that is not how an RV LP furnace works. 100% of the combustion gas moisture goes into the outside air, not just "most" of it. You offer no explanation as to HOW an RV LP furnace could possibly add moisture to the coach. Again, if you carefully re-read my post you will understand why you have condensation inside when using the gas furnace in cold weather. If is definitely NOT because of the LP furnace.

I have no interest in a running debate. You are simply misinterpreting/misunderstanding your situation. A short discussion with a knowledgeable HVAC person will enlighten you.

I am 100% CORRECT on both counts. Please read up a bit. Yes, normally we think heat pumps remove moisture in the room in cooling mode - just as you said. They also remove moisture from the heated space as the air circulates. That's why I installed a humidifier on every heat pump I've had in every home since 1972 when I bought my first home. The inside air of a house heated by a heat pump quickly becomes arid like the desert and that's a huge problem for me. I can certify in my humid environment of NW GA where humidity outside is frequently above 90%, winter or summer, the inside of the house will quickly fall below 30% humidity without the humidifier in the heat pump working. I check that regularly because of health condition. Right now I'll be glad to leave the "desert" of Denver. I left my portable humidifier at home so I boil water when we are in the RV in a steam pot at night to get the humidity up. If you had certain health conditions you most certainly would know these things. That's the only reason I have stayed in the Sunny South most of my life, the dry arid desert states are just unfriendly to my health. I did live in Washington St a long time on the western side, lots of humidity there too. Most folks who own a heat pump have a humidifier installed as well to regulate around 50% inside the home.

I also have LP at home for emergency heat after the blizzard of '93 left us with no power for three weeks. LP will definitely release moisture into the home. You should dehumidify running LP in extended modes. I do. If you do not dehumidify you will soon see moisture accumulate on the windows inside. I agree the combustion byproduct and a lot of heat is lost in the RV with the design of the LP furnace but it also introduces considerable moisture. The water is actually what causes a visible flame when LP is combusting. And...yes, in the RV most of it does go out and the vent and the heat exchanger does not accumulate it appreciably. It becomes a really big problem if you use an unvented heater like many do, gas logs for example and those wall heaters. If you use those the house will definitely get wet without a dehumidifier and you must open some windows or die.
 

TJLee089

2013 Itasca Reyo 25R
Absolutely correct but has nothing to do with heat pumps removing moisture, causing low humidity.

Here's a note from a HVAC company:

How to Combat Low Home Humidity During Heating Season

To make life more comfortable, preserve your home and its contents and help your heating system perform optimally, you need to add moisture to the indoor air. One option is to use portable humidifiers in different rooms of your home, but it’s essential that the output of each unit matches the size of the room or you could add too much moisture.

The most efficient way to increase home humidity is with a whole-house humidifier. These units are installed in a home’s HVAC system and add just the right amount of moisture to the air that’s circulating through the ductwork. A trusted HVAC professional is your best source of advice and assistance with sizing, selection, and installation.
 

TJLee089

2013 Itasca Reyo 25R
On this thread, #19, a post was made suggesting the heat pump was increasing coach humidity. That was also incorrect.

My response was:
The heat pump should not increase coach humidity. If so, something is wrong. In fact, with constant moisture in the air, relative humidity goes down as temperature goes up. In a closed space human bodies do give off moisture (800 ml/d according to this source) and raise the humidity. I did a rough calculation and found that 2 people during a 8 hour sleep cycle give off enough moisture to easily raise the relative humidity from 50% to 100% in a typical small RV space. That is part of the reason why the inside glass is wet in the morning, the other being falling outside temps.

This applies regardless of heating source.
 

billbo

Member
OK, absolutely ludicrous response. Of course the air circulation is removing the moisture. But then, I am only a patient who has studied this for the past 47 years or so, with professional help from physicians and from HVAC folks.

Given the fact that I also have extensive knowledge of HVAC and one son who has done it most of his working life - I don't need any further education from you.

I also decline to an ongoing running argument/debate. My complete statements are 100% correct. Everyone I know has a humidifier installed on their heat pump in the home. Yes. It is necessary to protect health, home and contents.

Just for grins I remember when we purchased our second Tiffin DP while speaking to Bob Tiffin we were discussing travel to some of the Western states. He stated to always run a humidifier while in those arid areas to prevent the wood inside the RV from being damaged. Me? Heck, I'm more concerned about my health.

The average healthy male gives off about 200 milliliters of water during an 8 hour sleep period, breathing. Yes, that is true and two people and a dog will definitely produce moisture on the windows in some conditions, temperature drop at night outside etc. You can actually call those functional bodies humidifiers. Normally opening a vent and allowing the air exchange will prevent the moisture accumulation.

As far as debating the technical reasons for a heat pump lowering the humidity in a home lets just admit it happens, which it does. I completely understand the technical functions of a heat pump and using one will lower the humidity in the home - enough said, whether you want to admit that or not does not matter it is just a known fact. It is not removing humidity the same way the unit does in cooling but it is drying the air to desert levels. It is certainly the exchange of air and air movement.

As far as using an unvented LP heater inside the coach - some are actually doing that but unless they got buried they opened a window. The debate is over.
 
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billbo

Member
The simple answer. Heating air increases it's capacity to hold water vapor which lowers the relative humidity. Relative humidity is simply the ratio of the current amount of water in the air at a given temperature relative to the maximum amount of water in the air at that same temperature. Then you can get into saturation vapor pressure which increases as temperature rises and on an on about pressure inside the house, outside the house, equalization of saturation vapor pressure and what the heck?

Bottom line, heat pumps decrease humidity in heat mode by a combination of effects. Those of us who are impacted use reliable measurements to keep humidity around 50%.
 

TJLee089

2013 Itasca Reyo 25R
Once again you are 100% wrong. Warming the air with a heat pump reduces relative humidity because warmer air can hold more moisture. It does not remove ANY moisture. It does nothing to absolute humidity, which is the actual moisture content of the air. Heat pumps in AC mode actually remove moisture from the air.

Life is too short to continue this discussion. Talk to the folks that service your home heat pump and LP systems. They will enlighten you.

To Summarize:
1. Heat pumps in heating mode (that simply recirculate inside air) and vented combustion heating sources (oil, gas) that pull the combustion air from the outside (RV LP furnaces) neither add nor remove moisture from the heated space.

2. Unvented combustion sources, such as gas stoves, gas fireplace logs, and freestanding kerosene heaters add moisture to the heated space.

3. The air in heated spaces becomes dry because of the exchange of cooler, drier outside air with warmer, wetter inside air by such things as vented bathroom fans, clothes dryers, and stove hoods; by opening doors and windows, AND vented combustion sources (oil, gas) that pull the combustion air from the heated space (inside) and vent the combustion gases to the outside.

I will stack my credentials against yours: B.S., M.S. Chemical Engineering. 30 years as a licensed professional engineer.


OK, absolutely ludicrous response. Of course the air circulation is removing the moisture. But then, I am only a patient who has studied this for the past 47 years or so, with professional help from physicians and from HVAC folks.

Given the fact that I also have extensive knowledge of HVAC and one son who has done it most of his working life - I don't need any further education from you.

I also decline to an ongoing running argument/debate. My complete statements are 100% correct. Everyone I know has a humidifier installed on their heat pump in the home. Yes. It is necessary to protect health, home and contents.

Just for grins I remember when we purchased our second Tiffin DP while speaking to Bob Tiffin we were discussing travel to some of the Western states. He stated to always run a humidifier while in those arid areas to prevent the wood inside the RV from being damaged. Me? Heck, I'm more concerned about my health.

The average healthy male gives off about 200 milliliters of water during an 8 hour sleep period, breathing. Yes, that is true and two people and a dog will definitely produce moisture on the windows in some conditions, temperature drop at night outside etc. You can actually call those functional bodies humidifiers. Normally opening a vent and allowing the air exchange will prevent the moisture accumulation.

As far as debating the technical reasons for a heat pump lowering the humidity in a home lets just admit it happens, which it does. I completely understand the technical functions of a heat pump and using one will lower the humidity in the home - enough said, whether you want to admit that or not does not matter it is just a known fact. It is not removing humidity the same way the unit does in cooling but it is drying the air to desert levels. It is certainly the exchange of air and air movement.

As far as using an unvented LP heater inside the coach - some are actually doing that but unless they got buried they opened a window. The debate is over.
 
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NYBobbo

Member
My 2 cents:

Heat pumps are used when temps are warmer (above 40), the warm air circulates making the entire rig more evenly heated then a cube heater. I believe, due to lower temp differentials when using HP (inside/outside ...perhaps a dew point issue) and air movement helps reduce condensation.

When much colder outside the furnace is needed - the output from the furnace is more localized and not circulated evenly around the rig, with the increased temp differentials and lack of even air flow I've noticed condensation on the windows to increase - usually when the propane heater is used.

I could be wrong, I may be wrong but I stand by my observations and subsequent thunkin on the subject.
 

Hosh

Navion 2018 24J
Well this thread is pretty lively. Anybody want to discuss the virtues of composting toilets, compressor fridges, bio diesel?
 

rollerbearing

Well-known member
Well this thread is pretty lively. Anybody want to discuss the virtues of composting toilets, compressor fridges, bio diesel?
IMHO, thumbs down on all three.
Ok - we get it. You two have by choice, or inability, decided to keep your rigs more or less stock. Fine. You've also expressed your opinions regarding other's mods. Fine & great.

I agree with Winterbagoal:

Sometimes it's expeditious to cut to the chase, and make your point. Then move on.
Of course, you'll be accused, by some, of being "uncivilized" if you choose this route.:bounce:
The key point is to "move on". Continuing to taunt, one up, beat a dead horse, etc. shuts down the discussion that others may be interested in. So ......time to contribute or move on.
 

TJLee089

2013 Itasca Reyo 25R
My last response to billbo included "Life is too short to continue this discussion." No one was shut out or shut down.

My rig is what it is by choice, not inablity.

Ok - we get it. You two have by choice, or inability, decided to keep your rigs more or less stock. Fine. You've also expressed your opinions regarding other's mods. Fine & great.

I agree with Winterbagoal:



The key point is to "move on". Continuing to taunt, one up, beat a dead horse, etc. shuts down the discussion that others may be interested in. So ......time to contribute or move on.
 

billbo

Member
What's really, really funny is the last two posts in our running discussion - Lee and myself. We said almost exactly the same thing yet I am again - 100% wrong. I said heated air holds more moisture per cubic volume which in effect reduces the relative humidity of the same cubic volume and yes, does nothing to reduce absolute humidity. So, we do agree. People and furniture do not benefit from absolute humidity - only relative humidity. The hotter you get the same cubic volume of air the more moisture it takes from that same cubic volume (it holds it). Air movement, air exchange all play a part as well.

Let's say credentials. Electrical Engineer, MS Physics, ya, da, da, Oh yeah, from MIT. One son is certified HVAC for many long years, the other is PhD Math from Auburn. OK, enough credential bashing.

We said the same thing and I'm 100% wrong? Nope, using the heat pump requires moisture to be added back into the air to increase RH for comfort and health.

I'm just as hard headed and anyone and once I even thought I was wrong - I was because I thought it so.
 
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TJLee089

2013 Itasca Reyo 25R
You stated that heat pumps in heating mode remove moisture. They do not.

My discussion was with you, not your sons.
 
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billbo

Member
Yes, I stand by that statement and explained exactly how it happens. My discussion is no longer with you until H%$$ freezes. Goodbye, oh, you dumped the "diplomas" etc., I was just playing with you. I suppose you didn't approve of my credentials? Have a good life. But ...I doubt it.
 

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