Fujitsu Multi-Position Air-Handling Unit
Patrick_OSullivan
| Posted in General Questions on
I’m trying to find the goldilocks indoor unit for part of my home (NJ, climate zone 4A). Total load calc is 19,306 Btu/h (heating) and 15,947 Btu/h (cooling). Air flow is 741 cfm @ 0.6 in. wc.
I do not want to oversize the system. At first glance, an 18,000 Btu/h unit would seem to be most appropriate, but it seems none of them can produce the required airflow for this situation. The downside of stepping up to 24,000 Btu/h is that the modulation capability of many of those units seems to not be ideal.
Another ‘design constraint’: if I can get to 18 SEER, 12 EER, 10 HSPF, and COP of 1.75 @ 5 F, I get $2,000 from the state.
I had thought the Fujitsu ‘mid-static’ unit (24RGLXD) was going to be a good option, but it misses out on the SEER requirement for the rebate.
Enter the AMUG24LMAS, a unit that is more like a traditional air handler, but seems to have decent modulation characteristics (minimum heating of 5,400 Btu/h @ 47 F).
Detailed specs: https://ashp.neep.org/#!/product/33397
Has anyone seen these in the wild or heard anything about them? Information is scarce online (I can’t even find a dealer that advertises selling it), so I’m wondering if it’s new product that’s not really made its way out yet.
Also open to recommendations of other units I may have missed in my research!
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Replies
The CFM requirement is just for sizing your ducts. You size the unit for the heat load. So if the 1.5 ton unit works, I would go for it.
For mid static units, you can also check out Mitsubishi, LG or Midea.
If this is a new build, it doesn't take much to decrease the duct losses a bit, which can get you down to a low static unit. There are many more options for these and are cheaper.
> The CFM requirement is just for sizing your ducts.
Well, at the end of the day, doesn't the system need a certain volume of air at a certain temperature in each room to adequately balance the heat flux in/out of the envelope?
So, there must be some minimum CFM for each room, and therefore a minimum CFM for the entire zone, and therefore a minimum CFM for the particular unit, no?
Less CFM just means that the duct air has to be hotter or cooler to satisfy the load. And with cooling, a common problem is too much air (unless some of it bypasses the coil).
Too little air will effect efficiency and can cause room-to-room balance to shift excessively (although that often happens anyway).
After I posted this, I think I realized my error. I was thinking of CFM as more of an output from the design rather than as an input to it. I think I should be instead thinking in the sequence of:
1. My design load is X Btu/h per room
2. The sum of the design loads for the zone is Y Btu/h.
3. The indoor unit selected provides up to Z Btu/h capacity by means of Q cfm of air at R in. wc.
4. Ducts then get sized to flow the proportional amount of Q per room without excessive pressure loss.
Exactly.
A spec to consider is how well the air handler matches the compressor output (CFM/ton) at low cooling loads. Most do poorly, almost eliminating dehumidification. But they don't publish this, so you don't know until you notice the dehumidifier running.
If they don't publish it, what's the best way to evaluate it? :-)
One can get some clues by looking at the compressor modulation range and compare to the air handler modulation range. But then there are things like "dry mode" and frequent manual adjustments.
Rebates aside, I have 2 - 12RGLX's in a 1:1 setup serving my 2nd floor and conditioned, unvented attic and I could not be happier with them. They are silent, they sip energy, they do not short cycle and they have done a very good job of managing humidity.
Great to know! Care to recommend your installer? If you'd prefer to share offline, I can provide contact info.
Hi Jonathan,
What does a 1:1 setup mean? Sounds like you have 2 outdoor units and 2 indoor units. Is that corect?
Mangesh,
1:1 or single zone means an outdoor unit is paired with only one indoor unit. This allows the outdoor unit to run as low as the indoor unit is capable of modulating down to. In a multi-zone setup there are multiple indoor units for each outdoor unit and the minimum operating capacity is limited to roughly the rated capacity of the indoor unit calling for heating/cooling at the time. The RGLX is only available in a 1:1 setup and I have 2 of the 12RGLX's systems serving the 2nd floor and 3rd floor unvented attic.
Great, that makes sense. It appears that Patrick (OP) has a single 18RGLX system serving both 2nd and 3rd floors, and so, I was a bit unsure. Do you mind sharing the square footage and load calculations for your 2 floors?
For my remodel of a single story house with ~1,600 sf, the HVAC installer has suggested a 4-ton 48LMAS1 system, and that seems highly oversized. Do HVAC installers perform load calculations for you, or does one need to get specialized companies to do it? My CA EN-1 energy compliance document is attached below, and it doesn't have much details on the load calculations.
I had 2 separate firms perform my Manual J, S and D. The first was an engineering firm that was also my HERS rater. The 2nd was the local Mitsubishi installer who was Passive House certified. The engineering firm came in around 14k BTU's for heating and the Mitsubishi installer was around 8k for each 1500 SF zone. The problem I had with Mitsubishi at the time was the static pressure limitation. I could not get good modulation with their air handlers that would meet the .7 wc static pressure requirements. Thankfully, before I had to make a decision Fujitsu came out with medium static units which fit the bill perfectly. My serial numbers are ...0000017 and 18 so I have some of the first units installed. I think the actual load numbers are probably somewhere between the 2 projections as the units do not cycle on warmer days and were able to meet the heat load requirements those few times this year when we hit design temps.
The load calcs for your project could very well be high, especially if performed by a HVAC installer not familiar with heat pumps or highly insulated homes. A good way to check is to ask for the detailed Manual J. This way you can confirm that a Manual J was actually done and you can look at the details for each room to confirm the correct wall construction, insulation, u-values, etc were used.
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Yes, I can share offline if you provide contact info.
Shoot me an email here if you don't mind: [email protected]
Now that the Fujitsu Multi Position air handler has been released and "in the wild" as Patrick called it for a few months does anyone have any thoughts on the unit? Fujitsu doesn't have much info out there.
I am considering it as an efficient, highly modulating solution for replacing my AC in my traditional ducted system in Albany NY. There are apparently significant rebates in NY for it also.
Oh how time flies. Couple of things:
1. I've seen an install of the multi-position unit via someone I follow on Instagram. Some comments indicated that it's truly a Rheem unit badged as Fujitsu. Not saying this is a bad thing, but it's interesting if nothing else.
2. I ended up selecting the 18,000 BTU/h Fujitsu mid-static units (ARU18RGLX/AOU18RGLX). So far, the system is absolutely excellent. It's covering my 2nd and 3rd floors. Observations thus far:
- It is stupidly quiet. Both I and the installers were having a tough time determining if it was actually on. Putting your ear to the return helps, but even then it's a whisper.
- The modulation thus far has been excellent. I have a separate temperature monitor that logs every 5 minutes and most of the time, it is maintaining temp within 1 degree F.
- No one has any experience installing them in ducted configurations in single family residential. The crew lead on my job was actually excited because it was something different than he'd ever done before.
Thanks to Jonathan Lawrence, I at least selected a company to install that has a very competent metal shop working behind the scenes for the installers. As an example, they had to build the supply plenum three times to get it perfect for the unit and field conditions.
Hi Patrick,
I'm looking at these exact units as a heat and cool option for my 1,400 sf home, but my home was built without any duct configuration in mind, there is no attic space whatsoever (all ceilings vaulted). Anyway, what size ducts did you use? maybe I missed it on the Fujitsu website but doesn't seem so specify duct size requirements, or if the indoor units could be placed under the house? I do have plenty of space there, tall pier foundation.
Thanks
> Anyway, what size ducts did you use? maybe I missed it on the Fujitsu website but doesn't seem so specify duct size requirements
Duct sizes are a designed part of the system. Everything starts with a room by room heat load calculation which then dictates how much air per room, which dictates size of duct per room, etc.
In my case, I have two main 14" x 7" trunks coming off of the unit.
> or if the indoor units could be placed under the house? I do have plenty of space there, tall pier foundation.
Is the space below your house insulated? If not, you really don't want to be putting ducts there. If so, it's probably doable. The particular unit I have needs some space below it so some components can be accessed. (In other words, it can't sit directly on a floor.)
Thanks for the response, I will be looking into these units further.
Hi Patrick,
Did you install a single medium static unit (ARU18RGLX/AOU18RGLX) for the 2 floors, or 2 units -- one for each floor?
> Did you install a single medium static unit (ARU18RGLX/AOU18RGLX) for the 2 floors, or 2 units -- one for each floor?
It's a single system serving the 2nd and 3rd floors.
Hi Patrick, do you mind taking a look at this other comment thread here? https://www.greenbuildingadvisor.com/question/thoughts-on-fujitsu-air-handler-with-seemingly-decent-modulation-characteristics?cid=198693&discussion=response#comment-198693
In your original post, how did you arrive at the load calculations? The EN-1 energy compliance document I got for my project lists the load only for the bedroom addition/expansion and not for the entire house (~1,600 sf) even though we're replacing the existing radiant floor heating system with a brand new heat pump HVAC system.
Also, per your comments, it appears that the multi-position air handlers (e.g., 48LMAS1) are rebranded Rheem systems? In that case, would a similarly sized Mitsubishi unit be better?
I have the multi position in my basement ready to install. Definitely a rebranded rheem. I’ll report back when we hook it ups
For what it’s worth, I have top floor apartment with the mid static. It’s next level.
Same outdoor units and electronics on both the mid static and Multi btw.
Any particular reason you went with the multi position in the basement given your success with the mid static? Just a question of form factor?
Form factor and I wanted backup heat in the first floor apartment. Easier to do with the multi position (it has a slot and the oversized toasters are less than 100 bucks... even for the 7kw. Wire costs are way more). I probably should have just gone with the mid static and slapped the backup in a duct. Guess I wanted to mix it up a bit :)
We have good luck with the Mitsubishi PVA units. They are expensive but seem to work great. We also really like the Fujitsu mid static units
Good to know. What area are you in? Since I see from previous posts that you're an HVAC contractor, I ask on behalf of the greater GBA community. I had a heck of a time finding an installer who even knew what I was asking for, let alone had installed one before.
We are in Iowa. I understand hvac contractors concerns with installing new equipment. The best way to lose money is to have a bunch of call backs on a complicated system. I went to school for microbiology so I love this stuff but I think you will be better off supplying a contractor a manual J and a manual S and then simply asking them to quote and install it per the MFG specifications. Asking HVAC contractors their opinions will Almost always result in them offering what they are comfortable with which is almost always oversized clunky equipment
> but I think you will be better off supplying a contractor a manual J and a manual S and then simply asking them to quote and install it per the MFG specifications. Asking HVAC contractors their opinions will Almost always result in them offering what they are comfortable with which is almost always oversized clunky equipment
I couldn't agree more. That's how I approach things (in a very nice manner) which leads to literally no one calling me back. :-)
Fortunately it all worked out and my system got installed well.
Patrick, would you be willing to share the name of the contractor you used? I think that both GBA and the contractor would be fine with having the name posted here, or if not I can post an email address. I'm in NH but trying to help my mom in NJ get her out-of-commission gas furnace replaced by a good cold-climate heat pump, and as might be expected the first bid was for a heatpump without any significant cold-weather capability, plus an oversized gas furnace.
Hi Charlie. I used Air Group (https://airgroupllc.com). I tend to shy away from larger subcontractors, but I received two referrals to Air Group (including one from here) so decided to give them a shot. My salesperson was Ron (contact info here: https://airgroupllc.com/residential-service-team/).
We had to tweak a few things along the way, but ultimately the system is performing well thus far and I genuinely believe the crew wanted to do a good job. The crew lead was excited he got to work with equipment he hadn't installed in residential before.
One of the most impressive things about them was their fabrication capability. They showed up the first day with the majority of my duct sections built, insulated, and labeled. Some components had to be custom built to field conditions after they got the location of the indoor unit finalized. They would call in specs and then a custom piece would show up later in the day or the next day.
Thanks so much Patrick! Glad to hear that it worked out well for you. And nice that that had such a good system for custom fabrication. Much better than resorting to sloppy flex ducts.
Patrick
Did you get NJ clean energy rebate on your install? I am also trying to get it but before that I need to get my load calculation correct and select equipment.
thanks
> Did you get NJ clean energy rebate on your install?
I plan to as my system qualifies, but I have not submitted the paperwork yet.
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Pactrick
How did you Qualify?
Requirements from the NJ Clean energy is :
Multi-zone, compact or centrally ducted SEER > 18, EER > 12, & HSPF > 10, COP 1.75 @ 5° F
Your set up seems to be only single zone ARU18RGLX/AOU18RGLX from your post #31.
Please see attached pictures.
Reason why I am asking is because I would like to use same system but 1 set per each floor.
Any information is appreciated and it will help me make a decision on my HVAC system.
thank you
It's "compact/centrally ducted".
> Multi-zone, compact or centrally ducted SEER > 18, EER > 12, & HSPF > 10, COP 1.75 @ 5° F
For this system:
SEER: 19
EER: 13
HSPF: 10.9
COP @ 5F: 2.22-2.45
See here: https://ashp.neep.org/#!/product/25348
Thanks for clearing confusion.
I was thinking it has to be multi-zone.
Patrick
Is this High heat model?
I hope it's ok to jump into this thread after a year-plus. I'll start a new thread if directed to ...
Are these multi-position air handler units meant to be dropped into a house with an existing system of ductwork ? I have an aging dual-fuel split system heat pump, that I'm sure will give up the ghost soon. I would love to replace it with a system that does not require propane (natural gas is not available in our area). Electric backup (heat strips) is probably not feasible for me, as my electrical panel is maxed out. It doesn't get that cold here (single digits are a rarity, sub-zero virtually unheard of) so something like:
https://www.ecomfort.com/Fujitsu-36LMAS1/p109257.html
https://ashp.neep.org/#!/product/33399/7/25000///0
... would be suitable.
> Are these multi-position air handler units meant to be dropped into a house with an existing system of ductwork ?
It all comes down to specs, but in general, yes. If the ducts were properly sized to begin with, it should work. People who have installed the air handler you linked to have remarked how similar (i.e. basically the same) they are to Rheem air handlers. Seems there is some part sharing/co-development going on (https://www.fujitsu-general.com/global/news/2016/16-V03-17/index.html).
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It seems like the issue that could arise, in conditioning an entire house (with one of these units connected to a conventional duct system) is that minisplits like to modulate the blower speed of the indoor unit to match the outdoor unit's variable output. If connected to a conventional duct system (iow, one originally designed for use with a conventional heatpump and/or furnace), and the indoor unit throttles down to a low airflow, the ducts for smaller rooms could be starved of airflow completely (if the airflow to the various ducts doesn't reduce proportionally to the airhandler output).
I've had this exact concern about modulating units in houses with less than perfect ductwork. Any experts care to weigh in on how critical good duct work is for modulating units? Are modulating units best avoided in older houses with sub-par ductwork?
These traditional air handler type units may not modulate the blower like a minisplit or compact ducted does. A quick look at the spec sheet shows what I expected: three normal fan speeds and an additional "quiet" speed.
Is that fewer speeds than a "regular" mini-split has ? Seems like the ductwork issue would still be critical at the low and quiet speeds.