Heat Pumps: Multi-spit vs 3x splits

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Scott3

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#314958 2-Jun-2024 16:10

Has anybody gone through this decision before?

Currently have a large heatpump in the lounge (primarily for winter heating).

Our house absolutely bakes upstairs (2x bedroom and a home office), currently make do in summer with a very old (noise, bulky & inefficient) hose out the window air con for our bedroom.

There is also another bedroom downstairs that we are considering tackling at the same time

But now that i have a job that is mostly work from home, we have decided to air conditioning the office is fairly essential, and we might as well do the other bedrooms at the same time As to get rid of the old portable air con.

In general we expect to run the Office aircon during the day in summer and our bedroom during the night. The other bedroom will only be needed when our child is doing homework, or during heatwaves etc (or perhaps to warm the room up after she has a bath in the winter).

I wanted lots of individual spits, so each unit has a full turn down range available, and I am concerned the multi-split compressor will be oversized for our typically operational case (1 room only), and like the idea that we can run a single air conditioner at ~0.9kW, or run every one at full noise (~2.5kW+ x 3)

That said, one vendor has quoted us Multispits, & it is dramatically cheaper (thousands) than what another vendor has quoted us for individual splits. I know it is a worse technical solution, but the cost saving is so substantial I am giving it serious thought. Quite appealing to have 1x big outdoor unit vs 3x little ones. And the multi split is big enough that it would get wired back to the switchboard vs the little units which would get tapped into the back of power outlets (we have 16A circuits and have tripped breakers on occasion)

We have also been quoted ducted (with zone control), ~$2k more than multispits. Shying away from this option as the ceiling space above our upstairs rooms gets crazy hot, and i am concerned about the heat gain through the insulated ductwork impacting efficiency.

We have our master bedroom downstairs, doesn't have the same heat issues as upstairs (and currently it is vacant, but we will move there when we expand the family). Have had an individual unit priced for this room, but potentially could also include it in the multisplit setup (but not the ducted setup).

Any thoughts on this? Has anybody regretted going multisplit?

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#3243800 2-Jun-2024 16:21

Also thoughts on brands?

For the individual units we have prices for Panasonic & Mitsubishi Electric. (Latter $400 more expensive). For context all our upstairs installs are complex, so the unit price is well under half of the total price. Same vendor quoted us Panasonic ducted.

Other vendor quoted us fujitsu ducted (incl zone control) & multispits. Spec sheet of the indoor fujitsu unit on the multisplit is noisier than the other brands.

Never been super happy with our big (~8kW), ~10 year old Panasonic in our living room. Fairly noisy, slow to start in heating mode, rusting screws, and recently an issue where it needs to be power cycled with the main switch if it hasn't been used in a few days. But it might be unfair to judge the brand based on an old unit.

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timmmay

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#3243802 2-Jun-2024 16:37

I had a Panasonic ducted unit for a month or so. It was so loud (indoor and outdoor) I made them take it out and replaced it with Daikin. That was in 2021, maybe they've improved, but I wouldn't touch Panasonic. I also don't like my Panasonic microwave. I just don't get on with Panasonic it seems.

Daikin and Mitsubishi are good brands - I have three Daikin, one ducted. I had a Fujitsu high wall for 7-8 years and it worked well, but the indoor unit was quite loud. My 15 year old Daikin 7kw highwall is still going ok. The one year old Daikin 2.5kw in my office is working great, and it has a very quiet mode that would probably work ok for bedrooms. The 10kw Daikin ducted with Airtouch zone control works well, though I've had to do a lot of automations in Home Assistant

I suggest you avoid ducted. Too much hassle for bedrooms, you need wall or door vents, there's often a spill zone (see my sticky thread for more on that). They are quiet though, if you get a good brand. Ceiling cavity heat not a big issue in my experience, even with R1.0 ducting it will be less efficient than high walls, but they have plenty of power so it'll cost a little more to run than a highwall but work fine.

Questions:

What are the approximate room sizes?
What are the min / max powers of the individual units and the multi-split unit?

mudguard

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#3243803 2-Jun-2024 16:51

I went with a multisplit at home. I'm probably 90% happy with it.
The reason was mostly to have a single outdoor unit. Our bedroom is directly above the lounge, and there is also a small deck off our bedroom.
One installer suggested a unit on that deck which I'd don't want.

With the multisplit there is a single unit at ground level and a single piece of capping on the outside wall which runs up to the second floor. It feeds the lounge unit as well. Fortunately the layout of the house means the heat pump units line up nicely in the two rooms.

Obviously (or maybe not so obvious) is that a multisplit cannot do two different modes (heating and cooling). This hasn't really been an issue for us. Because we are in Auckland and I run a bit hot we run the bedroom one on cold all night. Then about 5.45am the bedroom ones turns off, and the lounge one comes on heat until about 7am.

I went Mitsubishi for no particular reason other than the units inside look nice and my parents have had a couple over two decades without issue.

I also made sure I had the WiFi version. The app is easy (though the initial set up is not!) and we almost never use the remotes, which live in some draws. It's nice if we go away for the weekend as I can just turn them off for the weekend.
Same if it's cooler and we are out. It's nice to be able to turn them on remotely.

So as long as you don't need the different modes they work well. I'd have to look up the size of all the units. Our house is not very large.

tweake

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#3243804 2-Jun-2024 17:26

first thing is to work out what sizes you actually need in each room.

multi's are best used when most if not all heads are running. however you can use a smaller outdoor unit than you need. just means you won't get full performance from each when running all at once. but trying to get small enough multi is a problem. hell even trying to get small enough single can be a problem for small bedrooms.

with quotes, just check the labor. some guys will do the same install cost per unit, so no discount for getting 3 done at the same time.

rscole86

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#3243808 2-Jun-2024 18:08

I recently got a Mitsubishi multi installed. Two AP20's and an AP25 all off a single 3 port 5.4kW outdoor. It was significantly more expensive than the singles, but the benefit of a single outdoor was what we really wanted.

We run an AP20 6pm to 7am most days in the child's bedroom. The office and master bedroom are run as needed, we've run all three at the same time (yet).

As pointed out you can't run different modes (kind of), we've found you can heat and fan but not cool and fan, with two units concurrently. I've not tried other combinations, or seeing what three at once does.

We didn't even entertain going ducted due to the extra costs for a house I don't think it would really suit without serious money being spent.

Handle9

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#3243904 2-Jun-2024 22:41

Typically the main issues with multis are mode control and turndown/short cycling.

From what you've described mode control should be ok but I'd be concerned about short cycling. You've got a couple of ways of dealing with that but what I would seriously consider in your use case is undersizing the outdoor unit. If you are never going to run the units at full noise at the same time, you could get away with undersizing the outdoor unit and then still get turndown.

Of course that creates significant potential issues down the track if the use case changes but it would work rather well and further reduce the capital cost.

The other thing you could investigate is a dual head for the two bedrooms and an individual unit for the office space.

Scott3

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#3244012 3-Jun-2024 01:56

tweake:

first thing is to work out what sizes you actually need in each room.

multi's are best used when most if not all heads are running. however you can use a smaller outdoor unit than you need. just means you won't get full performance from each when running all at once. but trying to get small enough multi is a problem. hell even trying to get small enough single can be a problem for small bedrooms.

with quotes, just check the labor. some guys will do the same install cost per unit, so no discount for getting 3 done at the same time.

Sizing is always kinda hard. Calculators in NZ are all generally set up for winter heating, but other than a fan heater next to my wife (who grew up in the tropics) in our office, we don't really require any more heating than what drifts up our staircase from our long heat pump). Cooling is what I am after.

Numbers in bold below are from this calculator using the partially insulated setting.

https://www.mitsubishi-electric.co.nz/heatpump/how-to-choose-the-right-size-heat-pump.aspx

Upstairs Bedrooms are ~9.3 m^2 (1.2kW) each. Our portable air con in the bedroom is rated at 1.83kW, and takes the edge of the heat in summer, but never reaches it's set point. Of course this is an old unit so it may not be achieving it's rating, and a bunch of heat will leak into the room from the compressor, discharge duct, and air cycling via the window.

Upstairs Office is ~10.3 m^2. This is really the (summer) problem room Nor east facing skylight (opening), nor west facing window (non opening). Low sloped ceiling etc. a lot of thermal gain here. In winter a 1kW fan heater (regular fan heater on low) is fine to keep this room warm. (1.4kW)

Master bedroom (downstairs) is 14 m^2 (excl a walk in wardrobe and bathroom - bathroom has electric underfloor heating) - This room is much better thermally. Is 4 steps above the lounge so picks a decent amount of warmth from our lounge heatpump in winter, and is better ventilated and cooler than the upstairs rooms in summer. (1.9kW)

Split unit quotes are for:

4x Panasonic CS/CU-Z25XKR (rated 2.5kW cooling, 3.0kW heating)

There is 1 smaller size, in the Panasonic range, but minimum turn-down is the same. Do gain a little in efficiency though.

Or

4x Mitsubishi MSZ-AP25VGKD (rated 2.5 kW cooling, 3.5kW heating)

Of note, Mitsubishi Electric has recently released its first AP mini series heat pump. The installer said it was $150 cheaper, but recommended the AP25 over this model unless we needed the physically smaller size indoor unit, as the AP25 comes with wifi standard unlike the AP20.

The AP 20 has dramatically lower turndown (min capacity) than AP25, but is noisier and less efficient

Fujitsu (just for the master bedroom):

https://www.fujitsugeneral.co.nz/product/set-asth09knca

Not as quiet as the other brands when turned down low, and a touch lower cooling efficiency but otherwise the spec sheet looks.

Same brand also has a 2.0kW class unit

Ducted (2x upstairs bedrooms and study only):

One vendor quoted us a 6.8kW Cooling, 7.5kW heating ducted unit

The other quoted a 7.1kW Cooling, 8.0kW heating unit

Multi Spilt:

Outdoor:

Smallest unit that brand offers

https://www.fujitsugeneral.co.nz/product/aoth24kbca3

Indoor (I think our quote has an error in it as it references a spit unit, assume the one below is what was intended):

https://www.fujitsugeneral.co.nz/product/asth07kmcd

So the indoor unit's are a size down from what I was quoted as split units. Outdoor unit should be able to turn down low enough to run just one room, but that is pretty much the limit of the turn down (1.8kW, where the splits can turn down 0.6 - 1.1 kW depending on unit). Turn down should be just fine when running 2x units and great when running all three.

Not as quiet as the other brand units, but at less then 22dBA on low should be OK I guess.

Mitsubishi electric does offer lower power outdoor units, but the minimum run speed is worse than the Fujitsu...

Could also go up to the 4 port unit and include the master bedroom in the multi split, but then the minimum speed is way more than what one room will require:

Scott3

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#3244013 3-Jun-2024 02:11

Handle9:

Typically the main issues with multis are mode control and turndown/short cycling.

From what you've described mode control should be ok but I'd be concerned about short cycling. You've got a couple of ways of dealing with that but what I would seriously consider in your use case is undersizing the outdoor unit. If you are never going to run the units at full noise at the same time, you could get away with undersizing the outdoor unit and then still get turndown.

Of course that creates significant potential issues down the track if the use case changes but it would work rather well and further reduce the capital cost.

The other thing you could investigate is a dual head for the two bedrooms and an individual unit for the office space.

We are already on the smallest Fujusti multi outdoor unit. So no turn down advantage to breaking out a room.

Mitsubishi does have a 2 port unit. Only 0.2kW smaller than the 3 port, but much better turn down capability:

If only they made that with 3 ports, would be near perfect for what I am looking for.

Our office has a lot of heat load, so I am more concerned about Short cycling at night with our bedroom (Unless it is really hot we are unlikely to run our child's aircon overnight as she has eczema).

Could potentially do a pair of these doing two rooms each, as the turn down is comparable with a single AP25. Suspect this won't be very cost-effective though.

timmmay

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#3244027 3-Jun-2024 08:12

On one hand, the individual units will be more likely able to run on very low power without cycling constantly. However, in my office when on low fan I don't find that a problem. Maybe that affects lifespan at least in theory? Our kitchen unit is too large so it cycles regularly and it's 15 years old. BUT four lots of outdoor units and trunking will be quite ugly.

The multi-split will likely cycle regularly. This Daikin can support two indoor units and goes down to 1.2kw, so you'd need two. I can't find the minimum output for their larger unit.

I think it might come down to asthetics. If you can live with lots of outdoor units, including the hassle of painting around the ducting, it's a technically better solution. I think I would probably go for multi-split.

eonsim

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#3244034 3-Jun-2024 09:21

We also went for a single multi-head (3 port unit with only 2 heads) unit a couple of years ago, had it set up to manage the NE and SE bedrooms.

Works well even though there can be a couple of degree difference in temperatures between the two rooms (NE 1-2C warmer). Use Home assistant to control them, and effectively have them set to mimic each other so they stay in sync, though can have slightly different target temperatures. Unit maybe a little oversized considering it's running only 2 heads off a 3 head unit, but it does cool and heat the rooms very quickly.

Only real complaint is that the Panasonic heads are a noisy and there temperature sensors are terrible so effectively need to dial in corrected temps via home-assistant and secondary temperature sensors within the rooms. If we were doing it again would have gone with Mitsi or Fujitsu as the unit's we have for those in other parts of the house are noticeably quieter.

timmmay

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#3244040 3-Jun-2024 10:15

eonsim:

Only real complaint is that the Panasonic heads are a noisy and there temperature sensors are terrible so effectively need to dial in corrected temps via home-assistant and secondary temperature sensors within the rooms. If we were doing it again would have gone with Mitsi or Fujitsu as the unit's we have for those in other parts of the house are noticeably quieter.

Friends don't let friends buy Panasonic heat pumps.

Scott3

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#3244044 3-Jun-2024 11:03

timmmay:

On one hand, the individual units will be more likely able to run on very low power without cycling constantly. However, in my office when on low fan I don't find that a problem. Maybe that affects lifespan at least in theory? Our kitchen unit is too large so it cycles regularly and it's 15 years old. BUT four lots of outdoor units and trunking will be quite ugly.

The multi-split will likely cycle regularly. This Daikin can support two indoor units and goes down to 1.2kw, so you'd need two. I can't find the minimum output for their larger unit.

I think it might come down to asthetics. If you can live with lots of outdoor units, including the hassle of painting around the ducting, it's a technically better solution. I think I would probably go for multi-split.

We already have one heatpump, so adding four outdoor units would take us to 5 total. They would be quite spread out. 2 at the front of the house, 2 at the rear, 1 at the non-accessed side (rear and side I only ever really go to mow the lawns), so I don't think that is a deal breaker aesthetically.

I'm more interested in the cost savings of less outdoor units and how the unit will be big enough to justify wiring back to the switchboard, rather than being hung off the 16A power circuits.

The House exterior was painted under a year ago, so shouldn't have to deal with exterior re-painting for ~15 years.

Scott3

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#3244047 3-Jun-2024 11:09

Generally seems like there is a lot of love for multi-spilts. I was expecting to be warned off them.

I am supprised that they are more expensive in some cases, giving the pricing I have received.

timmmay:

eonsim:

Only real complaint is that the Panasonic heads are a noisy and there temperature sensors are terrible so effectively need to dial in corrected temps via home-assistant and secondary temperature sensors within the rooms. If we were doing it again would have gone with Mitsi or Fujitsu as the unit's we have for those in other parts of the house are noticeably quieter.

Friends don't let friends buy Panasonic heat pumps.

Not super happy with our big one. (noisey, vanes get stuck sometimes, had to swap out rusty screws, sometimes requires power cycle on outdoor switch).

But being $400 cheaper like for per unit vs Misti electric adds up fast when buying four of them.

And I have stayed in accommodation with little Panasonic air conditioners (in the tropics so cooling only), and they seemed fine, nice & quiet etc.

tweake

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#3244068 3-Jun-2024 12:46

Scott3:

Sizing is always kinda hard. Calculators in NZ are all generally set up for winter heating, but other than a fan heater next to my wife (who grew up in the tropics) in our office, we don't really require any more heating than what drifts up our staircase from our long heat pump). Cooling is what I am after.

Numbers in bold below are from this calculator using the partially insulated setting.

https://www.mitsubishi-electric.co.nz/heatpump/how-to-choose-the-right-size-heat-pump.aspx

Upstairs Bedrooms are ~9.3 m^2 (1.2kW) each. Our portable air con in the bedroom is rated at 1.83kW, and takes the edge of the heat in summer, but never reaches it's set point. Of course this is an old unit so it may not be achieving it's rating, and a bunch of heat will leak into the room from the compressor, discharge duct, and air cycling via the window.

Upstairs Office is ~10.3 m^2. This is really the (summer) problem room Nor east facing skylight (opening), nor west facing window (non opening). Low sloped ceiling etc. a lot of thermal gain here. In winter a 1kW fan heater (regular fan heater on low) is fine to keep this room warm. (1.4kW)

Master bedroom (downstairs) is 14 m^2 (excl a walk in wardrobe and bathroom - bathroom has electric underfloor heating) - This room is much better thermally. Is 4 steps above the lounge so picks a decent amount of warmth from our lounge heatpump in winter, and is better ventilated and cooler than the upstairs rooms in summer. (1.9kW)

i would use the 2kw models for the bedrooms.

i have two panasonic 2.5kw models in similar sized rooms and i wish they where smaller. both overshoot heating temps (probably due to being to big but possibly also temp sensor issues as i think they are designed for taller rooms than what nz typically has). noise of fans is an issue. the smaller units have slower quieter fans which is a lot nicer in bedrooms and office. with small rooms you tend to get blasted by the cool air.

also don't forget humidity. you want the aircon to run for long periods so it can work as a dehumidifier. heatpumps are usually tuned for best cooling and less dehumidification. with auckland humidity and air leaky homes, humidity control can be tricky. however reducing fan speed can increase dehumidification. this is also why smaller heatpumps can be better.

the office usage is probably a bit better if your using the office during the day. ie have aircon running early in the day rather than trying to cool down a hot room at the end of the day, which is what most tend to do.

upstairs may be a factor depending on how well the door is shut. cool air sinks. so if you leave the door open a lot, you will need a bigger model as your cooling downstairs as well. if so, seriously think about heating/cooling the entire house as one.

if you have a werid shaped room, check the required install height of the unit, and that you can actually install it at that height. (you might struggle to find that height in the specs, i only found it in the install manual.)

tweake

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#3244069 3-Jun-2024 12:54

Scott3:

Generally seems like there is a lot of love for multi-spilts. I was expecting to be warned off them.

generally i warn people off them. they are a hack. but they do come in handy for tight spaces when you do not have the room outdoors for multiple units.

they come with efficiency issues, depending on how they are run. also if it fails you loose all of them. they are more suited to doing big rooms where you have multiple heads running exactly the same. small rooms are the worse situation because we don't get the really small models. (you showed the new mitsi 2kw one, they actually make a model smaller than that but its not sold here).

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