Refrigerant Quantity query?

[Rapserv]

Wanting to install a Daikin split system in my caravan to replace the pretty useless, noisy, inefficient Dometic unit currently in use.
I note that the specs on both units state 3500w cooling output however, the Dometic uses .5L of R405C and the Daikin 1.25L of R410A. Does the fact that the daikin uses far more refrigerant mean that it will do a better job of cooling, particularly in the hotter weather.
I currently find that the Dometic really struggles to keep things cool (basically equivalent a single room...in the 20ft caravan) when outside temps are around 40-45C and around these temps seems to be almost blowing not much cooler than warm air.... I know this is getting fairly warm, but I also know that the Daikin airconds used in some of the outback mining villages I work in do a good job of keeping things cool ... sometimes too cool :cool:
The Dometic I have used for a couple of years since new and it has never seemed to me to be that cool. It's ok in moderate temps (apart from being extremely noisy) but once things really heat up it just does not perform as you would expect. I recently had the unit regassed and this seems to have made no noticable difference. The Dometic unit is, according to their specs, the largest in the range and should be more than suitable for the job. Just won't handle sustained high outside air temperatures.... even though in the shade.

[FreezerGeezer]

Wrong question, really. They're 2 different refrigerants, so it's like asking if a Land Rover and a Falcon will do the same job.
The answer, of course, is yes. But... ;)

I think the important thing for you to look at is what the refrigerating capacity of the system is at the ambient temperatures you're experiencing. Basically, the higher the ambient temperature, the less effectively the condenser (the outdoor coil in cooling mode) will work.
Refrigerant selection, condenser coil design (& size) condenser fan selection will all have an effect on how high an ambient the system will work in, effectively.

The simple thing to do is look to see what others have in their caravans (especially if they're the same model as yours, so the materials & insulation properties will be the same) & see what does & doesn't work in your environment.
Be aware that while Daikin is very good kit, any faulty PCB will require replacement of all the outdoor PCB's and the condenser fan motor(a), which gets very expensive post warranty. I wouldn't automatically let that put me off, but it may be worth considering.

[Gary]

To properly evaluate the performance, we would need to start with the entering and leaving air temperatures for both the outdoor and indoor coils (measured near the coils).

[FreezerGeezer]

Absolutely Gary.
I suspect that what Rapserv has is similar to these: http://www.waeco.com.au/forms/CatalogueBrochures/web-C_130104_AirCon8Pager_JCN.pdf
Which are more or less a window rattler. I note that the website does not provide data on maximum operating conditions. Although you'd expect Waeco to know the domestic market backwards.
Hence my initial reply not requesting the usual info.

Rapserv, have you made sure that the filters and both coils are really, really clean? Just wondering as you are in one of the dustiest environments on earth. ;)
If you can give Gary the data he requests, perhaps we can advise if there's something not right with the Dometic. A model no. would be good. And when it's running in cooling, what's the state of the suction pipe at the compressor once it's been on for 10 minutes or more - dry, sweating, frozen? The suction is the larger pipe connected to the compressor.

[Rapserv]

Wrong question, really. They're 2 different refrigerants, so it's like asking if a Land Rover and a Falcon will do the same job.
The answer, of course, is yes. But... ;)

I think the important thing for you to look at is what the refrigerating capacity of the system is at the ambient temperatures you're experiencing. Basically, the higher the ambient temperature, the less effectively the condenser (the outdoor coil in cooling mode) will work.
Refrigerant selection, condenser coil design (& size) condenser fan selection will all have an effect on how high an ambient the system will work in, effectively.

The simple thing to do is look to see what others have in their caravans (especially if they're the same model as yours, so the materials & insulation properties will be the same) & see what does & doesn't work in your environment.
Be aware that while Daikin is very good kit, any faulty PCB will require replacement of all the outdoor PCB's and the condenser fan motor(a), which gets very expensive post warranty. I wouldn't automatically let that put me off, but it may be worth considering.

thanks for the reply.
I am aware that different refrigerants perform differently, however, I thought that the quantity of refrigerant in the Daikin which is substantially more than the Dometic unit must be doing something different to make it worthwhile having that much refrigerant in there in the first place.
I would have thought that the liquid part of the refrigerant in the system would have a better chance of remaining cooler than if a minimal amount was used.
Seems to me that the Dometic (model: B3253 Roof Top Airconditioner) is a lighter duty system, designed for occassional use in not particularly extreme conditions unlike the Daikin units which seem to have all components upsized and designed for constant extreme use.

[Rapserv]

Absolutely Gary.
I suspect that what Rapserv has is similar to these: http://www.waeco.com.au/forms/CatalogueBrochures/web-C_130104_AirCon8Pager_JCN.pdf
Which are more or less a window rattler. I note that the website does not provide data on maximum operating conditions. Although you'd expect Waeco to know the domestic market backwards.
Hence my initial reply not requesting the usual info.

Rapserv, have you made sure that the filters and both coils are really, really clean? Just wondering as you are in one of the dustiest environments on earth. ;)
If you can give Gary the data he requests, perhaps we can advise if there's something not right with the Dometic. A model no. would be good. And when it's running in cooling, what's the state of the suction pipe at the compressor once it's been on for 10 minutes or more - dry, sweating, frozen? The suction is the larger pipe connected to the compressor.

thanks for your reply.
The Dometic unit is similar to that in the brochure you noted and as you also stated ... a window rattler .. although this one rattles pretty much everthing in the van and is so noisy that the TV volume needs to be way louder than it should be. It's amazing that the glossy Dometic brochure states as one of the units benefits is it's 'Ultra-Quiet 3-speed-fan' ... possibly is.. you just can't hear it above the noise from the compressor.
I regularly check and clean the filter and coils. The model no is B3253 and to check the suction pipe at the compressor I will need to remove the top cover which forms part of the airflow system.
As I mentioned in my original post, this unit has performed this way since new.

[FreezerGeezer]

At a guess, the split system is going to have a larger internal volume than the Dometic, hence a significantly larger refrigerant charge. It may be able to move more air, which I'd expect would provide noticeably better cooling for you.

[Rapserv]

At a guess, the split system is going to have a larger internal volume than the Dometic, hence a significantly larger refrigerant charge. It may be able to move more air, which I'd expect would provide noticeably better cooling for you.

Thanks again for the reply,
These were also my thoughts. At the end of the day the greater volume would do a better job of cooling, the unit is more energy effecient and whisper quiet compared to the Dometic.:cool:

[Gary]

It's not about refrigerant volume, it's about coil surface area and air flow.

[The Viking]

Hmm,
As stated above, see what works for other caravans the same size as yours.
Potentially, you are sitting on about 21m2 of floor space there which would give you little more than 150W/m2 from a 3500W unit.
150 W/m2 is what we are looking at in office space here in UK, nowhere near your ambient conditions and also not with all four walls, roof and floor exposed to the ambient temp and solar gain. Well worth looking in to before you bite the bullet and buy a new unit.

Also, before you decide on a specific brand/unit do check what the maximum ambient temperature they will operate in. I know some brands specify for ambient temperatures below 35ºC whilst other manufacturers, like Samsung, have special ranges of A/Cs for higher ambient conditions.

:cool:

[Rapserv]

Hmm,
As stated above, see what works for other caravans the same size as yours.
Potentially, you are sitting on about 21m2 of floor space there which would give you little more than 150W/m2 from a 3500W unit.
150 W/m2 is what we are looking at in office space here in UK, nowhere near your ambient conditions and also not with all four walls, roof and floor exposed to the ambient temp and solar gain. Well worth looking in to before you bite the bullet and buy a new unit.

Also, before you decide on a specific brand/unit do check what the maximum ambient temperature they will operate in. I know some brands specify for ambient temperatures below 35ºC whilst other manufacturers, like Samsung, have special ranges of A/Cs for higher ambient conditions.

:cool:
Taking into account the internal cupboard space, fridge, qs bed, shower, etc I think we are looking at about 15m2 ... ie about 230W/m2.
The reason I mention the Daikin is that I am familiar with their cooling capabilities in an Australian outback mining environment... and also, I have access to a second hand unit in excellent condition at very minimal cost. ;)
Specs on the Daikin show an ambient working range for the outdoor unit from -15C to +46C.
I think from what I have seen that the Daikin will cool very well to at least 46C before its performance starts to degrade, whereas, with the Dometic unit it is really starting to struggle from around 35C and pretty much pumping out slightly better than warm air at 40C.

[Rapserv]

It's not about refrigerant volume, it's about coil surface area and air flow.
wouldn't the larger quantity of refrigerant in itself indicate a larger cooling surface area and airflow?

[sedgy]

HEY RAPSERV,
cooling your caravan is , me heating a caravan in the uk in winter with a single candle
it aint gona work cos there is insouciant insulation in the caravan, ( do you get the drift?)= sedgy
(ok the candle is an exaggeration )

[Gary]

wouldn't the larger quantity of refrigerant in itself indicate a larger cooling surface area and airflow?

No, it wouldn't... even if we were comparing units with the same refrigerant, which we are not.

[FreezerGeezer]

As Gary says.
The volume of refrigerant in a system is determined by several factors, including the length of the pipe run, the size of the coils, the size of pipe, minimum velocities for oil return, the capacity & type of compressor, etc. etc.
All of which is determined during the design process. The design refrigerant quantity is actuall the last (or almost last) item to be calculated.