Single-Zone Heat Pump with Multiple Air Handlers
I’ve read that multi-zoned heat pump systems are less efficient than single zone with multiple modulating air handlers. But I cannot seem to find any information on manufacturers sites about using a single zone heat pump with multiple handlers. Is this because it’s so self-explanatory that they don’t even bother mentioning it, or because it’s an unusual, non-industry standard installation? Or maybe I’m just not understanding what I’m reading.
My situation is as follows. Zone 5 – NY. I’m looking to heat 1000sqft home with 2 bedrooms, living room and kitchen. Due to the layout 4 separate units are recommend and I agree. The contractor keeps pushing for separate condensers for each air handler for efficiency. Efficiency is important to me as well, but I’m not about to put 4 condensers around a 1000sqft home.
I do not ever anticipate the need to be heating a room when another is calling for cooling so I believe a single zone with modulating handlers should work. But damn if the literature doesn’t confuse me. Does anyone have clarity on this? Best would be if anyone could provide examples of the model/part number or spec sheet of a single zone condenser unit that can do this. I’m looking specifically at Mitsubishi systems.
Alternatively I’m leaning towards a ducted single zone 30K BTU. The SVZ-KP30NA & SUZ-KA30NAHZ model, but it seems much less efficient than the wall/ceiling units. This may or may not be true when we start talking about multiple zones with a single heat pump system.
Thanks for anyone who can cut through the fog.
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Four one-to-one ductless units for 1,000 sq feet would be a bit much for sure. In the bedrooms, they would probably not be able to modulate low enough. You don't say what climate zone you are in or what your heat cooling load is. However, it sounds like you are on the right path to look at a ducted unit. Depending on your floor plan and how complicated it makes the duct work, one ducted unit might work. You might also consider a ducted for the bedrooms and a wall mount ductless for the kitchen/dining area. On our first floor we installed a Fujitsu Slim ducted 12k for the bedrooms, bathrooms, and living area. For the kitchen and dining room (open floor plan), we installed a 9k ductless wall mount. It works great and the family is happy we've improved the air flow to the bedrooms.
Thanks, we are zone 5 and single story simply floor plan. My original plan was actually 2 slim ducted units. The quote I got for that was ~25% higher than the single ducted, which itself was slightly higher than the wall mounted proposal. Unfortunately I'm sort of on a budget but I am still considering the slim ducts for 2 reasons:
1 - Way better modulation. The 18K BTU units will modulate down to like 6K and the the 12K down to 4K.
2 - Dehumidifying - The slim ducted units can operate in a dry mode and actually pull a decent amount of water. Like 4 pints per hour. Our house has a humidity issue.
I think the threshold question is: Can a single zone heat pump be connected to multiple air handlers? And, if so, how.
The SUZ-KA30NAHZ can do almost 3 tons of heat in your climate. That would put your place at around 32btu/sqft, which would be the heat load for an uninsulated barn.
I would try to figure out your actual heat load and go from there. If you have fuel use data for the existing equipment run through the steps here:
https://www.greenbuildingadvisor.com/article/out-with-the-old-in-with-the-new
A 4 zone multi split is a bad idea, 4 one-to-one units is better but ugly on the outside.
I think your options are either a fully ducted unit for the whole house or a two zone setup with a wall mount in the living room and a ducted unit for the rest of the house.
I agree with you on the sizing. While I haven’t done a Manual J measurement both my contractor and I had originally planned to go with the SUZ-KA24NAHZ and supplemental electric heat for the coldest days. This unit would modulate to a much lower BTU in cooling and I think would perform better overall. And it dehumidifies better. But….it doesn’t qualify for NY rebates due to the low COP @ 5F 🤦♂️ . I save $3k with the KA30 unit.
I’ll try go back to discuss the 2 zone solution if the contractor will still talk to me after so much back and forth. I think I would do 2 ducted SEZ units though in that situation. I guessing you would recommend 2 single zones instead of a multi zone. People really seem to dislike the multi zones.
Given the fact that multi-zone heat pumps are less efficient than single zone heat pumps, the worst thing you can do with a multi-zone heat pump is oversize. I believe that much of the bad reputation on multi-zone heat pumps is due to oversizing. Of course oversizing applies to single zone heat pumps too. Per the thread below "The Multi-Zone Heat Pump Issue", the Mitsubishi rep notes that some in Norway select heat pumps at 80% of design load.
Personally, being sensitive to noise, I can barely stand the noise of one heat pump, along with the foot high, five foot long and two foot wide pile of ice. Minimum set backs are 5 ft, which translates to 10 ft min between houses. I can hear my neighbors furnace when outside and my other neighbor's AC when inside (2o ft away). The primary bedroom is quiet at night in winter with only a minimal swoosh from a ducted air handler. In summer, there's the condensate pump buzz, which isn't too bad (condensate gravity drain would solve that). HVAC "comfort" is more than temp/humidity. My "right-sized" three zone hyper-heat system provides sufficient comfort/cost.
From the thread: "The Multi-Zone Heat Pump Issue"
https://www.greenbuildingadvisor.com/article/multi-zone-heat-pump-issue
Dana: But I think that when you’re trying to cover all the seasonality in these far northern states, you really want to be very close to exactly the same amount of heating load, or up to 120%. Along the same line, one of the things that I’ve bumped into in some of my reading from the Heat Pump Association in Norway (that has a lot of experience in cold climates and has been doing this for a long time), is that you can find documentation where they say the ideal efficiency for the front cost of the system and the overall operational performance of the system comes when you size it to around 80% of the heating load of the house…
I'm definitely not one of the fans of multi splits, I live with an oversized 3 zone one and regret installing it.
They can be made to work and do work quite well but they have to sized correctly. This means not only matching the outdoor unit to the overall heat load of the house but also matching each head to each zone. As long as you do this, they do work well.
For a single story structure without anything with major variable loads such as a sunroom, a single zone will work great. There is no point for paying more for a multi zone even if there is a small efficiency gain if you go with two one-to-one setups.
You can also look at the Carrier branded Midea units.
https://ashp.neep.org/#!/product/33276
The Mr Cool Universal is also a great cold climate heat pump for not much money. It also comes in a DIY version with quick connect refrigerant lines.
Understood, a lot of variables with multi splits. The home layout was suitable for a three zone and an energy consultant was required for a HERS rating who had a long time working relationship with the HVAC installers, which provided multiple checks on the heat load.
The plot is 27 months of data, average kWh/day versus average monthly temperature F. Baseline consumption is about 5 kWh/day or 150 kWh/month (28.6 kBTU/h rated hyper-heat with three ducted zones: 15k, 12k and 9k). Quite linear for heating.
Thanks for the nudge to Carrier. Looking at their product line and seems really impressive and good warranty. Curious where the catch is. There’s always a catch…right?
I like DIY stuff but this will be primary heat source and I’ve heard that some contractors won’t even touch the Mr Cool DIY systems.
You sure the SUZ-KA24 doesn't qualify for the incentives, but the SUZ-KA30 does? They have nearly identical performance specs at 5F on the NEEP database
Make sure you’re looking at the hyperheat model. Needs to end with HZ. They have the standard NA model but of course you’ll see a huge drop off in performance @ 5F. When I search the SUZ-KA24NAHZ model I’m not able to find the unit paired with the SVZ-KP24NA indoor handler on the neep ccASHP list. I assume this is due to the low COP @ 5F. Spec sheet here:
https://www.mitsubishitechinfo.ca/sites/default/files/SB_SVZ-KP24NA%20_SUZ-KA24NAHZ_202103a.pdf
I do notice that it passes muster when paired with the horizontal mid static PEAD indoor unit though 🤔. Maybe I’ll look into that.
Before you start to look at equipment, you need to figure out what your heat loss really is. Most cases it is better to even undersize slightly and install a small strip heater that only runs a couple of days in the year than oversize and have the unit cycle most of the time.
I would not be surprised that your place can be carried by the 1.5 ton hyper heat, and it can definitely carry the place with the small strip heater.
https://ashp.neep.org/#!/product/34578
The PEAD is a good option but it doesn't look like a "standard" furnace. It can also only be installed horizontally. You'll probably have to pay a premium to hook it up even through it is not all that much extra work.
Does anyone have experience with Flair duct controllers or similar devices that enable you to have multiple zones with a ducted mini-split?
I had two small rooms with very different heating needs as one of them gets a lot of afternoon sun. And we were considering installing a pellet stove in one of the rooms, so we needed two zones. At the time the only way to do that seemed to be to put in a multi unit with two heads. The result is that the cycles are very short.
Now it appears that Flair and Keen sell thermostatically controlled dampers that also communicate with the mini-split to ensure that both rooms are the desired temperatures. Has anyone used devices like those?