How many frigs A/C for 50m2?

Hi all,

I found this site while searching for a knowledgable community that may be able to help give me some unbiased sound advice where otherwise I've read and received so much conflicting information it's driving me crazy.

I have a little single story property in the Spanish countryside with a ducted A/C system. The system needs replacing, as it 1. it doesn't work properly, 2. we want something more economical to run, this current beast of a unit often exceeds our contracted power allowance (4.7kw) causing the breakers to trip which can be very inconvenient as I also work from home.

The system vents air to 4 rooms, totalling 50m2. When I try to determine which modern units are most suitable, different sites suggest different units, when I speak with local providers, they suggest I still need something that can deliver ~10'000 frigs like my current unit, which goes against everything else I've seen when I look up what I need for an area of 50m2,

One guy said, I have to still look for a 10k frig unit because the ducts are currently designed for the 10k unit I have now and a unit with less that 10k won't be able to move air around properly..
I could understand that more if I had a large surface area, but this house is very small so I wonder how much truth is there.

Someone else suggested to change from the ducted system and instead go with a multi-split unit.

Any advice would be very much appreciated!

Thanks,

Hello daveb and welcome to the forum.

You don't give a make or model number of your existing system or tell us how old it is, what refrigerant it uses, etc..

When sizing A/C, we work out the total heat gain into the rooms/space and match a system to handle this load.

Here in the UK there is an organisation that publishes data for building services that is referenced to an extent by designers involved in heating, plumbing, ventilation A/C etc. called CIBSE (Charted Institute of Building Services Engineers) and the Americans have a similar organisation called Ashrae.

These between them have a wealth of information regarding calculating heat loads/losses. Here are a couple of links to have a look at
https://www.ashrae.org/
https://www.cibse.org/Knowledge/Guides

Without knowing your budget or system usage, it is difficult to say wether you should just replace the existing ducted unit or change to individual splits. I suppose one of the benefits of individual splits is that you can switch any 1 or more system on at a time, depending on which room you are in. This will obviously be cheaper than cooling all rooms when empty rooms do not need cooling (i.e. bedroom during the day).

All modern split type systems now are inverter driven which allows the compressor to match output to heat load quite precisely, thereby drawing less power. Another benefit is that modern systems provide both heating and cooling.

I have a relative that has lived in Spain for the last 24 years. He was spending 500 euros a year on logs for his little log burner to heat the kitchen area (A/C elsewhere). 2 years ago, he ripped out the log burner and installed a small split which cost 430 euros. Running costs from then on are no where near 500 euros/year. Win win all round :)

Hi Frank, thanks for your reply I'll take a look at those links you provide.

To answer your question on what we currently have in place, it's a Daikin RZP125DV1 external unit with the internal counterpart.

Re' usage, typically(if it was working correctly) it would be in use daily(and throughout the night) during summer for A/C and on throughout the day only for heating during winter, spring and autumn the device can be off except for odd exceptional days.

Electricity prices have rocketed here during these last few months, we're now paying up to 500 per month in electricity, so for this reason we're also looking at solar, but we know for sure the A/C unit is a massive consumer so swapping this out for something more efficient and economical is a must.

Attachment 16110

That's a chunky unit, a very good age and brand. If that was here your load would be about 2/3 of that at 9kw (assuming 180w/sqm).

I'm with Frank, any modern heat pump inverter will use less electricity than that, with the benefit of not dimming the lights every time it kicks in! As with anything using less of it will cost you less, is the building relatively well sealed? Can you use blinds etc to keep sun out of rooms, keep doors&windows closed etc.

Ask the companies sizing for you to give you the duty in Kw, they are right about the duct work, indoor would need to be fairly close to old unit pressure wise. If a multisplit can be installed i would suggest it, it means you only cool the areas you are in and hence use less power. Units are fairly cheap over there, i would go with what will be cheapest and most efficient to run.

Thanks Al. Seems a shame to consider changing from the ducts to installing units in each room but if it makes a bit difference to the running costs then it's worth me looking into. The house and the ducts are isolated to a corridor that joins all the rooms, so there's not a lot of duct work, the furthest vent from the A/C unit is probably 6 meters, so I wouldn't have thought that's considered too long.

This is a unit one company suggested:

https://expertclima.es/mitsubishi-el...ontrol_wifi-no

This is one that said I need a machine that supplies 10'000 Frigs because my old unit was 10'000. For a total of 50m2 space, it seems like I have to pick a unit that is double the power than I really need. With such little duct area, maybe it's more sense to adjust the ducts so it can work better with a less powerful machine.

With the ducted you are cooling areas you possibly are not using, it is up to your self but my opinion is wall mounts and only have on what is needed.