Reverse Cycle Air Cond Query - not automotive.

Fordman

Fordman

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The nearest this gets to be being automotive related is that it is installed in my caravan/camper. :)

My Coromal camper/fold-down caravan has a very neat Heater/Air Conditioner installed under a bed with 3 x 65mm ducts to 3 outlets in the van.
It's a nice unit, in my opinion, brand is Truma Climaster, this is the installation & owner's manual if you are interested:

This van is about 16 years old but has had very little use, and been in storage for about 10 years. (Might I add that buying this van is the probably the worst financial decision I have ever made, not because it's a bad unit, but because we just never got the opportunities for extended holidays and various family commitments. I bet I'm not the only person to ever say that about a caravan purchase!). But I am now restoring it to a good saleable condition, and finding that most of the built in units are working OK which is a bonus.

OK, my query is with the reverse cycle unit as above. It is only designed to work when connected to 240v AC, not 12v or gas. Now when I first checked it last week, I concluded that the fan was working (blowing good air) but the compressor/gas system had failed/leaked, because it was not cooling - I had a thermometer at an outlet as one does in a motor vehicle, expecting it to drop to under 5°C, but nothing after 15 minutes or so. Same with switch set to Heating - just cool air.
THEN I READ THE OWNERS MANUAL!! (What?, I hear you say :mallet:)

Interesting - (a) the air conditioner will not operate below 20°C, and (b) the heater will not operate below 4°C (which is when you would really need it - but fortunately in our climate - not often).

As it was probably about 15°C when I was testing the air cond - I may have concluded incorrectly.
So I tried the heater again and after about 10 minutes I did note a slight warmish air at the outlets, so I left the van closed up for an hour with the heater running - and voila - 26°C in van with 18°C ambient - that took me by surprise - so the heater is working fine, it's just a small unit (1.9kw heating) and took a while to heat up the room.

I finally get to the question of the day, for the knowledgeable among you.
It's a reverse cycle unit, so if the heater system works, am I to presume that the air cond should also work when the ambient is in a range that it will operate (ie, over 20°C)? As far as I can see, the same compressor works as a heat pump or an air cooler, so I am hoping that it will.

Hoping for a 22/23° run over the next few days so I will give it a go, but it might be a while before we get an actual "hot"day.

Obviously if the air conditioner/heater works, and I have already confirmed the 3-way fridge works well at least on 240vAC, then it bodes well for a good price when I sell the van hopefully in the next few months, and less expensive repairs.

And hey, I don't need any comments on the fact that a camper has an aircondioner!

Cheers.
 
my understanding is when its on cold it removes heat from the inside ,puts it on the outside[like a fridge ] ,when its on heat it douse the reverse, moves heat from outside puts it on the inside [reverse cycle .] so i think your assumption it right ,provided its working within the above mentioned parameters
 
Agree. If you've proven you have refrigerant circulating and working in one cycle, the other should work as well. It looks like it's purely down to the effective temperature ranges.
 
pugwash said:
my understanding is when its on cold it removes heat from the inside ,puts it on the outside[like a fridge ] ,when its on heat it douse the reverse, moves heat from outside puts it on the inside [reverse cycle .] so i think your assumption it right ,provided its working within the above mentioned parameters
Click to expand...

The Gonz said:
Agree. If you've proven you have refrigerant circulating and working in one cycle, the other should work as well. It looks like it's purely down to the effective temperature ranges.
Click to expand...

Thanks, it makes me feel better knowing that I probably won't need to remove the unit and have it serviced/gassed/repaired at some cost. Fortunately I read about the parameters before proceeding. (y)(y)(y)
 
Look for a diagram of an AC reversing valve online. It reverses the refrigerant flow so that the evaporator and condenser coils swap function. The compressor function isn't altered.

The refrigerant gas determines the range it works in. i hope it is available.
 
Well now you have heated it up to 26 degrees.... if you're really concerned, set the temperature to 18degrees and flick it over to A/C and see if it blows refrigerated air. I'm sure it will.

Caravan A/C's aren't really that great. I fitted a domestic split system to ours.
 
DoubleChevron said:
Well now you have heated it up to 26 degrees.... if you're really concerned, set the temperature to 18degrees and flick it over to A/C and see if it blows refrigerated air. I'm sure it will.

Caravan A/C's aren't really that great. I fitted a domestic split system to ours.
Click to expand...
You could be right, but I have presumed it has an outside temp sensor - maybe not, I'll check it out.
And yes, although it is fairly small, it is only a 14ft caravan. After it heated up after say half an hour I thought that's ok, it would be very comfortable on a cold evening.
The interesting point was that it won't heat under 4degC, and the explanation in the manual was something like a heat pump is not efficient in very cold temps. I thought of some comments in the water heating thread. Apparently it is the same principle.
 
Fordman said:
You could be right, but I have presumed it has an outside temp sensor - maybe not, I'll check it out.
And yes, although it is fairly small, it is only a 14ft caravan. After it heated up after say half an hour I thought that's ok, it would be very comfortable on a cold evening.
The interesting point was that it won't heat under 4degC, and the explanation in the manual was something like a heat pump is not efficient in very cold temps. I thought of some comments in the water heating thread. Apparently it is the same principle.
Click to expand...

You just carry a fan heater. You have paid so much for a caravan site somewhere, efficiency of the heater is irrelevant. a fan heater will heat a caravan in mere minutes, where as a heat pump will be endlessly reversing its cycle and getting nowhere fast if its cold out.

if you free camp, a diesel heater is the magic thing.
 
As said, the refrigerant characteristics determine performance in cold weather. For low temperature performance you can get heat pumps that run carbon dioxide R744.
 
seasink said:
As said, the refrigerant characteristics determine performance in cold weather. For low temperature performance you can get heat pumps that run carbon dioxide R744.
Click to expand...

I find these interesting, as how do they stop the outside unit turning to a block of ice ?
 
Go and find one of these coldroom jobs - https://hussmann.com.au/products/sy.../transcritical-co2-condensing-unit-2hp-mt-lt/

The Panasonic blurb for units like these is:
"The 4HP model (OCU-CR400VF8) is a 7.5kW (2.1TR) medium-temperature system with evaporating temperatures from -20°C/-4°F to -5°C/23°F. It can operate between -15°C and 43°C ambient temperatures (5 to 109°F)."

Scanden sell one running a domestic water heater.
 
Quote from specs of my caravan unit (as per link in first post):

Refrigerant R 407C Refrigerant content 470 grams Compressor oil
Diamond MA32, 300 cm³
Maximum inclination of vehicle during operation 5°

Operational limits +4 °C to +45 °C​

  • An icing sensor prevents impermissible formation of ice on the evaporator
  • A temperature switch prevents excess current flow and excess temperature at the compressor.

Just for information.
Hopefully it is not going to require any refrigerant anyway
 
Hi.

I did some reading up in this.

As others have noted, I think the selection of R407C refrigerant is the main reason for the operation limitations. It seems that R407C is the substiture for R22. R407C is a blend of three other refrigerants. I suspect that the limits are measured with a sensor on the outside air ducting. I suspect that the limits are also to prevent high discharge pressures on the compressor, for either damage prevention or limiting high current draw on compressor startup?

The COP is rather low for a heat pump. Heating output 1.9kW / electrical input 0.95kW = COP of 2. ie; you are getting two units of heat output for nearly one unit of energy intput. As Shane says, you would nearly be better to run a 2.4kW fan heater for heating, as most caravans run the 15A 3.6kW electrical supply, and you usually don't pay for it.

Cooling output 2.2kW / electrical input 0.95kW = COP of 2.31. ie: you are getting just over two units of cooling output for nearly one unit of energy intput. Thesedays most inverter split systems achieve COP in the high 4's.

I am not an expert, but maybe a change of refrigerant might improve the COP performance, but I suspect the existing operational limits will be part of the contol / logic circuit and not easily modified.

If it is working I would leave it well alone.

PS: for our family and circumstances I tend to agree that caravans are a poor investment.

PPS: While travelling up to Canberra in my car recently I got talking to a guy at a toilet stop on the Hume. I asked what his fuel consumption was. He told me that on his trip to date from Brisbane down to Tasmania and return, his average was 21.5 Lt/ 100km. My car was achieving 5 Lt/100km. He had a Landcruiser V8 diesel, with a large offroad/highriding single axle caravan. So 21.5Lt x $2.30per Lt diesel = $49.45. So it was costing him roughly $50 for every 100km that he towed that van. So a return trip from Brisbane to Hobart is 5,000km, so that would cost 5,000km / 100km x $50 = $2,500. Thats a lot of hotels, without the investment of $100k for the tow vehicle and say $80k for the van. Thats also not taking into consideration any nights he paid to stay at a caravan park, which is usually every 4 days or so.

Cheers.
 
caravaning is great for grey nomads that travel for extended periods of time. this way the cost of fuel to tow is less of an issue .... and young families (if they can afford it). It is NOT a cheap holiday like it was 40 years ago. If I take my family away in a caravan, a lot of places want $60+ a night plus $15.00 per child :eek: especially in school holidays. So your paying $100+ per night for a dead patch of grass in a caravan park somewhere. So for a short holiday, towing the block of flats .... probably getting 35L/100 (on lpg) you aren't caravaning to save money. Especially when caravans are worth so much money.

I have no idea how anyone with a young family these days can go on a holiday, let alone afford the rent/repayments on a house ( not to mention a caravan and car capable of towing the caravan). All I can assume is there is some extremely wealthy people out there ..... Or more likely people with staggering debts hanging over them ( ie: house loan, car loan x 2, caravan loan, boat loan, jetski loan, motorbike loan .... etc).
 
BTW: You should have thrown the caravan on the market over the last 2 years ..... values have increased massively over the last two years, but everything seems to be slumping now with interest rates going up. I could easily have sold our ancient ( 1985 ) caravan for $20,000 over the last couple of years. I probably should have, but its good to know its there if we need it.
 
DoubleChevron said:
caravaning is great for grey nomads that travel for extended periods of time. this way the cost of fuel to tow is less of an issue .... and young families (if they can afford it). It is NOT a cheap holiday like it was 40 years ago. If I take my family away in a caravan, a lot of places want $60+ a night plus $15.00 per child :eek: especially in school holidays. So your paying $100+ per night for a dead patch of grass in a caravan park somewhere. So for a short holiday, towing the block of flats .... probably getting 35L/100 (on lpg) you aren't caravaning to save money. Especially when caravans are worth so much money.

I have no idea how anyone with a young family these days can go on a holiday, let alone afford the rent/repayments on a house ( not to mention a caravan and car capable of towing the caravan). All I can assume is there is some extremely wealthy people out there ..... Or more likely people with staggering debts hanging over them ( ie: house loan, car loan x 2, caravan loan, boat loan, jetski loan, motorbike loan .... etc).
Click to expand...
Hi.

On the first point, I agree with your comments. Back when we did it a bit, I purchased a $5k secondhand Jayco Swan, that needed some maintenance. We did usually on trip a year at Easter, no further than the Murray. We could tow it with my usuall work car. After ten years I sold the Jayco for $5.5k. I didn't even have the van insured.

On the second point, I suspect a lot of boomers might have sold their house / downsized and put the profit into a tow vehicle and caravan. Some of these rigs will cost nearly $200k.

Also to enable caravaning, need to consider the cost of running a large tow vehicle for the other 11 months of the year, and whining about the high cost of fuel. Plus insurance for the van, and somewhere to store it.

Cheers
 
Sold my old van for a bomb 2 years ago.
I then purchased a small LUNAR Ariva 12 ft caravan, with air con and central heating with shower and toilet.
Weighs 900 kg. Does the two of us grey nomads nicely.
Opening the manual, yes I do read manuals, the first page had in bold print.
This van is "Safe at speeds up to 130 kph" :)
Has GTS stripes from the early 2000's
Overtakes those $200K rigs so easily using 12l/100km at a pacy 110km/hr
gts.jpg
 
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