Portable A/C

I have never owned one but did sell them and do understand how they work.
Those who are saying that the single hose models are inefficient for cooling because they are exhausting air that has already been cooled and the exhausted air will be replaced by hot outside air via infiltration are correct.

In our part of the country (MN) any time well sell a high performance range hood (over 700 cu ft per minute) the building inspector will make the homeowner also install a make-up air system in their home to replace the air being drawn out of the home by the range hood. The make-up air system will include a furnace to heat that air in the winter.

The actual comparison with roof A/C would be if the condenser blower were sucking air from the living space to cool the condenser and then exhausting it to the outside.

Living space air must be somehow replenished.

12,000 BTU "net" cooling = ~8,000 BTU.

Big Katuna wrote:

BUMPY wrote:
if air is exhausted from the single hose, it must also enter someplace. that place will be leaks around windows etc. if there is no additional air intake via the second hose. roof acs do bring in fresh air into their air exchange plenum and exhaust to the outside. the inside air circulates past the cold heat exchanger.
bumpy

Bet you $10 you are incorrect. Roof ACs do not pull outside air into the coach. They pull interior air across the cold evaporator and put it back into the interior. Outside, it pulls pulls air across the hot condensor to remove heat.

You ARE correct that a single hose portable ac will pull air into the coach somewhere.

that is exactly what I tried to say, perhaps ineffectively. yes roof ACS do not pull air into the coach, they pull it into the air/heat exchange area of the unit.
bumpy

Can't comment on two hose units, but my single hose units are kicking butt in humid mid GA. Mine evaporate the condensation be "flinging" it at the condensor to help it transfer heat and through evaporation and exhaust it out with condensor air.

Heat pump mode augmented with furnace, or some other type living space heat?

Single hose would definitely outperform.

On the other hand these is a great deal of confusion over the "heat pump" term when applied to the low end A/C market. In COLD weather a 2 hose A/C heap pump, reverse refrigeration cycle, would NOT match the performance of single hose A/C heat pump. Like those new "heat Pump" hot water heaters when installed inside the living space, the single hose unit would operating "parasitically" from/off the axillary heat source.

That's why those new heat pump water heaters should NEVER be installed within heated living space.

Robbing Peter to pay Paul, as it were.

wwest wrote:

rgatijnet1 wrote:

wwest wrote:

Sorry, you simply CANNOT exhaust living space airflow without it being replenished. Mother Nature, you know, HATES a vacuum.

If I were you, I would not get one.
Since I am me, and have several years of experience with my portable heat pump/AC unit, I think I will keep it. Nothing beats actual experience, which is why I got rid of my double hose unit and went with a single hose unit. :B

1.) In the 2 hose unit the incoming outside air, HOT air, passes through the CONDENSER in order to COOL the pressurized refrigerant within. A portion of that airflow bypasses he condenser and is used to cool the compressor. All of intake air, now heated, is then EXHAUSTED via the second hose. Yes, there is often 2 blower motors, but the gain in system efficiency easily overcomes any extra heat, if any, generated in the process.

Using a single blower means the blowers must run at the highest speed required of either. HOT outside, the condenser cooling blower MUST run at HIGH speed. This conflicts with the evaporator blower since the slower it runs the greater will be the cooling gain through the evaporator.

2.) As the linked article states:

A single hose A/C takes some of the cool air from the room and uses it to cool down the compressor(***1)..and then shoots it outside. Not only does this waste a significant proportion of the already-cooled air, it creates what is known as "negative pressure" in the room. In order to replace the air lost through the exhaust, warm air from adjacent rooms(***2) will seep in, which decreases the overall cooling efficiency.

***1. Typo.. should say condenser, compressor cooling is secondary. Condenser needs to remove ~10-12,000 BTU into that airflow, compressor heat represents maybe 300 BTU.

***2. And ultimately from the HOT atmosphere outside the home/RV.

I appreciate the very thorough explanation of how the units work, but I also know that I have used both the two hose and single hose units in my RV, in both cold Winter climates and hot Summer locations. I know that there is theory and there is actual experience. I got rid of the 2 hose AC/heat pump and kept the single hose unit because it worked the best OVERALL, for the weather conditions where we use it. As I mentioned before, nothing beats actual experience.
You have had good luck with the 2 hose unit so you should keep using it and I will keep using what works best in my RV.

rgatijnet1 wrote:

wwest wrote:

Sorry, you simply CANNOT exhaust living space airflow without it being replenished. Mother Nature, you know, HATES a vacuum.

If I were you, I would not get one.
Since I am me, and have several years of experience with my portable heat pump/AC unit, I think I will keep it. Nothing beats actual experience, which is why I got rid of my double hose unit and went with a single hose unit. :B

1.) In the 2 hose unit the incoming outside air, HOT air, passes through the CONDENSER in order to COOL the pressurized refrigerant within. A portion of that airflow bypasses he condenser and is used to cool the compressor. All of intake air, now heated, is then EXHAUSTED via the second hose. Yes, there is often 2 blower motors, but the gain in system efficiency easily overcomes any extra heat, if any, generated in the process.

Using a single blower means the blowers must run at the highest speed required of either. HOT outside, the condenser cooling blower MUST run at HIGH speed. This conflicts with the evaporator blower since the slower it runs the greater will be the cooling gain through the evaporator.

2.) As the linked article states:

A single hose A/C takes some of the cool air from the room and uses it to cool down the compressor(***1)..and then shoots it outside. Not only does this waste a significant proportion of the already-cooled air, it creates what is known as "negative pressure" in the room. In order to replace the air lost through the exhaust, warm air from adjacent rooms(***2) will seep in, which decreases the overall cooling efficiency.

***1. Typo.. should say condenser, compressor cooling is secondary. Condenser needs to remove ~10-12,000 BTU into that airflow, compressor heat represents maybe 300 BTU.

***2. And ultimately from the HOT atmosphere outside the home/RV.

One thing I forgot was the exhaust tube. DH does sheetmetal for a living, the intricate pieces. We took out a screen in the kitchen window, DH made a sheet of metal that size to fit with the hole and slides that the hose slips into with a tight fit. Looks great! Have a screen attached to hole so no bugs can get in. When not in use we close the slat windows. Never had problems with water coming in or cool air escaping. Condensation hose to the sink.

Big Katuna wrote:

snip wrote:
If the OUTSIDE temp is cooler, I really don't need an AC unit do I?

Yes, as the sun turns your RV into a solar oven. In Florida, when its 95 out, the RV can get 120 degrees inside. Higher in cars.

Thankfully, with my roof top and portable ac units, I always stay nice and comfortable at about 70 degrees, even in the hot Florida sun we have today.

snip wrote:
If the OUTSIDE temp is cooler, I really don't need an AC unit do I?

Yes, as the sun turns your RV into a solar oven. In Florida, when its 95 out, the RV can get 120 degrees inside. Higher in cars.