Mini-split ductless heat pump -location of installation

[tonycastec]

I am planning the installation of an 18,000Btu Fujitsu mini split condenser outside my house. The most convenient location is under a deck with about 4 feet of headroom between the dirt and the deck joists. The space is well ventilated and accessible for service. Clearly you can't stand up straight but it would be quite comfortable to do service work there.
Is there any 'rule' about mini split condensers needing more headroom ?

The proposed location already has the 240v connection and requires only 10 ft line set.
The alternative location without the deck clearance issue requires a new 45' run of 240v wiring and 25ft+ line set.
Thanks for any suggestions about where I can find answers.

 

[mo2872]

Fujitsu, nice! My Sanyo came with clearance requirements in the manual, you might check in yours(I know, against the grain of being a guy)...LOL.

 

[rlitman]

I installed an 18kBTU Fujitsu AC (actually a Friedrich, but it's just the same unit rebranded) in my house, and recall detailed clearance requirements in the manual (which I don't have handy).

As I see it though, the biggest issue will be the unit's efficiency, if it cannot pull in cooler air. As well as you think the unit is "well ventilated", I can assure you that it will be warmer under the deck when the unit is running, and if it's sucking in the warm air, that will hurt your efficiency. One thing you can consider, is moving it closer to the side of the deck, where the intake side (you must determine which way the fan turns to know which way the airflow goes), is closest to fresh air.

 

[tonycastec]

The only clearance specified is 18" .I think they mean 18" on all four sides.It is too unusual to have to specify overhead cleanace ? I agree,it is all about ventilation .The question is: is 4 feet enough?

 

[rlitman]

Is 4 feet enough, depends on airflow. You could meet the letter of the clearance requirements by putting it in a walk-in closet too. That doesn't mean it will work right.

4 feet of headroom is way more than the space many air conditioner units are squeezed into, so yes, from a serviceability standpoint, you'll be fine.

I'm picturing a patch of unused dirt, under the entire area of the deck. If so, you'd only be extending your lineset a few feet, if you placed it just within the perimeter of the deck, and you wouldn't be strangling it with heat.

 

[tonycastec]

Thanks for your comment. I'd rather rely on your experience than vague instructions translated poorly from a distant manufacturer.

 

[Jackfre]

I think you will find the line set length to be to short for that model. 9,12&15 have a min 9', 18 and up is 15'. To short is bad for the compressor. Do not put it on the ground. Suspend it off the deck or wall mount it with an Airtec or Slimduct bracket. I was going to put in an 18 at my old house, but chose a 15. It was within about 1500 btu on the cooling side but had a much lower min. Output. With modulating equipment that is a big factor.

Friedrich is made by Fujitsu, but it is not as full featured as the Fujitsu brand. That varies by model.

 

[tonycastec]

Jack,
The reason for suspending the unit above the ground (instead of the conventional concrete pad) is to improve air flow through the condenser?
Thanks,

 

[HVAC Phil]

Jack,
The reason for suspending the unit above the ground (instead of the conventional concrete pad) is to improve air flow through the condenser?
Thanks,

Also helps keep dirt out of coils and off the ground since it is a heatpump(ice buildup).

 

[tonycastec]

Phil,
Thanks.That makes sense but no ice in LA !
Plenty of dust potentially . I'll cover the dirt under the deck around the condenser to reduce that problem.

 

[tonycastec]

Here is the link to the site someone kindly mentioned above.Very useful:
http://airtec.rectorseal.com/slimduct_main.html

 

[Jackfre]

It figures! I just put a dual system in my daughters house in LA. Left this morning with a spare condenser mount. As Phil points out, the dirt is one of the biggest issues. I was on a call some time back where a ground mounted system malfunctioned. It had been installed for 10 days. The lower half of the coil face was completely blocked with mud due to the splashing of heavy rain runoff. Preserve your investment.

 

[mpire]

I got an expensive wall mount bracket that I didn't use.

I ended up getting two big blocks of concrete then setting them in a bed of gravel and then pouring concrete around them to hold them in place.

 

[redsky49]

As a "rule of thumb", the less obstructed, the better.

For typical round condensing units/heat pumps with condenser fans blowing up:
Unobstructed above, with three feet clear to the sides. You can often shorten this up on the one side that faces the house, but code will require three feet from all electrical service sides. Your serviceman will thank you, as will the condensing unit.

For the "suitcase" type condensing units that are used on many of the Asian systems, the space requirements are somewhat less strict and these units are more forgiving of overhead obstructions, as long as the expelled heat will not have any chance of being re-circulated to the unit. Again however, maintain adequate service clearances.

It is normally not necessary to elevate the installation of the outdoor unit as long as some common sense is used. Pre-fabricated concrete pads are suitable bases for 90% of installations. Unless you have localized flooding or some other issue, plop the unit on the ground. Exceptions to this might include beach areas where blowing sand is an issue or where theft or aesthetic issues come into play. And of course, do not place under the downspout.

In any case, always follow the manufacturer's recommendations for installation requirements.

In primarily cooling applications (such as L.A.), I like to place the outdoor unit on the north or shaded side of the building (being careful not to place the unit under the master bedroom window or other noise sensitive area). The difference in cooling performance between 95 degree entering air and 105 degree entering air can range up to 10% reduction in residential applications.

Improper placement will frequently result in head pressure issues, with the units cutting out due to the built-in safeties, shortened service life, or reduced performance due to the higher entering air temperatures. Again, follow the manufacturer instructions.

As to the comment that the refrigerant lineset could be too short, that has no basis. In the event that excessively long linesets are required, accessory kits are generally available to avoid slugging of refrigerant - particularly at startup.

As always, offered only as opinion

 

[tonycastec]

Redsky
Thank you for your thoughtful suggestions.It certainly seems you understand these issues very well.Thanks for taking the time to share.

 

[Jackfre]

As to the comment that the refrigerant lineset could be too short, that has no basis. In the event that excessively long linesets are required, accessory kits are generally available to avoid slugging of refrigerant - particularly at startup.

As always, offered only as opinion

On the Fujitsu MS' there is a min line length requirement. I think that on the inverter MS' that is fairly common, but is definitely the case on Fujitsu. As to "over-long" line sets, no accessory kit is available on a Fujitsu MS. You have a variable speed compressor, condenser & evap fan. No add on kits are going to complement the software that is driving these things. Min/max line set lengths are critical components of a proper install on your Fujitsu.

 

[mpire]

According to my A/C Guru, the mini-split comes pre-charged for 25' linesets. If you want to go longer, no problem, but you will have to add refrigerant.

The unit I got for my garage on closeout was low on refrigerant by 19oz when I installed it. It apparently had lost 2/3rds of the refrigerant sitting in the warehouse for 6 years.

 

[redsky49]

On the Fujitsu MS' there is a min line length requirement. I think that on the inverter MS' that is fairly common, but is definitely the case on Fujitsu. As to "over-long" line sets, no accessory kit is available on a Fujitsu MS. You have a variable speed compressor, condenser & evap fan. No add on kits are going to complement the software that is driving these things. Min/max line set lengths are critical components of a proper install on your Fujitsu.

As long as you are using the manufacturer's linesets, you should have no problems if the installation guidelines are followed. If you are creating your own (not generally recommended), here is a nice illustrated guide to refrigerant piping, based on ASHRAE standards:

http://www.mcquay.com/mcquaybiz/literature/lit_systems/AppGuide/AG_31-011_120407.pdf

Remember too that refrigerant piping is not the same as standard copper tubing as is used in plumbing systems.

I don't have intimate experience with every unit manufactured by every manufacturer, so I am trying to provide a general response based on my experience. I have no direct experience with Fujitsu General America, though I have been spec'g Mitsubishi for quite some time, as well as the Sanyo and Frederich or GE mini splits. I did try to get access to the installation manuals for Fujitsu but they limit access and I wasn't that interested in trying any further.

The potential problems with refrigerant and poorly designed piping are numerous, which is why for (especially) residential applications, pre-packaged piping is made available by the manufacturer. I can't imagine any reasonable way to screw this up if installation requirements are followed. In my experience, issues arise due to excessive length or elevation of piping, especially if the unit has been turned off and there is some natural trap in the piping where the refrigerant will pool and/or the lubricant will settle out or is in too high a concentration.

As with any internet advice(?), take my responses with the same grain of salt as you would from any other poster. And read the instructions!

As always, offered only as opinion

 

[rlitman]

As long as you are using the manufacturer's linesets, you should have no problems if the installation guidelines are followed.

For one thing, the mini-split manufacturer does not provide, or sell, linesets.

For another, I was informed by a professional when I did my installation that this is NOT true for pre-made linesets either.

If you look closely at the flare nut provided with pre-made linesets, the shoulders are much more recessed, and the whole nut is probably 1/3 lighter than the one that is supplied by the manufacturer with the mini-split, which supplies a nut with much more blockish shoulders.

Most mini-splits are using R410a nowadays, and the pressures found in such a system are much higher than you'll find with R22, for which the pre-made linesets are designed.

The heavier flare nuts are important to getting a lasting flare seal on an R410a system, but to use them, you must cut off the pre-made flare ends, and make your own. Also, if you look closely at the instructions, the torque requirements for these flare nuts are to a pretty demanding spec. I did mine using a crowsfoot wrench on a torque wrench.

 

[redsky49]

At risk of going off topic, but...

As I said, I am not familiar with the manufacturer mentioned. They do not appear to have a presence in engineering offices, at least in my area. A number of copy cat mini-split units are now in the market place, most if not all sourced from China, that I am not willing to be a beta tester for, so I stick with track proven brands.

Mitsubishi, the pioneer in this area with their original "Mr. Slim" units, do indeed provide linesets of various lengths:

Request InformationCompare Items Results Per Page :
Results 1 - 25 of 34 1 2

Item #

Item Name

Description

Length

Tube Size

Insul

MLS143812T-15 Refrigerant Tubing Sets N/A 15 ft 1/4 x 3/8 in 1/2 in
MLS143812T-30 Refrigerant Tubing Sets N/A 30 ft 1/4 x 3/8 in 1/2 in
MLS143812T-50 Refrigerant Tubing Sets N/A 50 ft 1/4 x 3/8 in 1/2 in
MLS143812T-65 Refrigerant Tubing Sets N/A 65 ft 1/4 x 3/8 in 1/2 in
MLS141212T-15 Refrigerant Tubing Sets N/A 15 ft 1/4 x 1/2 in 1/2 in
MLS141212T-30 Refrigerant Tubing Sets N/A 30 ft 1/4 x 1/2 in 1/2 in
MLS141212T-50 Refrigerant Tubing Sets N/A 50 ft 1/4 x 1/2 in 1/2 in
MLS141212T-65 Refrigerant Tubing Sets N/A 65 ft 1/4 x 1/2 in 1/2 in
MLS141212T-100 Refrigerant Tubing Sets N/A 100 ft 1/4 x 1/2 in 1/2 in
MLS145812T-15 Refrigerant Tubing Sets N/A 15 ft 1/4 x 5/8 in 1/2 in
MLS145812T-30 Refrigerant Tubing Sets N/A 30 ft 1/4 x 5/8 in 1/2 in
MLS145812T-50 Refrigerant Tubing Sets N/A 50 ft 1/4 x 5/8 in 1/2 in
MLS145812T-65 Refrigerant Tubing Sets N/A 65 ft 1/4 x 5/8 in 1/2 in
MLS145812T-100 Refrigerant Tubing Sets N/A 100 ft 1/4 x 5/8 in 1/2 in
MPLS385812T-10 Refrigerant Tubing Sets N/A 10 ft 3/8 x 5/8 in 1/2 in
MPLS385812T-15 Refrigerant Tubing Sets N/A 15 ft 3/8 x 5/8 in 1/2 in
MPLS385812T-30 Refrigerant Tubing Sets N/A 30 ft 3/8 x 5/8 in 1/2 in
MPLS385812T-50 Refrigerant Tubing Sets N/A 50 ft 3/8 x 5/8 in 1/2 in
MPLS385812T-65 Refrigerant Tubing Sets N/A 65 ft 3/8 x 5/8 in 1/2 in
MPLS385812T-100 Refrigerant Tubing Sets N/A 100 ft 3/8 x 5/8 in 1/2 in
MAC-397IF-E Controls MA and contact terminal interface N/A N/A N/A
MAC-399IF-E Controls M-NET control adapter for Mr. Slim MSY and MSZ models N/A N/A N/A
PAR-21MAA-G Controls Deluxe MA remote controller (Requires MAC-397IF-E for ductless indoor units) N/A N/A N/A
MAC-2300FT Filters Anti-allergy enzyme filter N/A N/A N/A
MAC-415FT Filters Anti-allergy enzyme filter N/A N/A N/A

Just a portion of the available accessories (data courtesy of and property of Mitsubishi)

The other mainstream manufacturers are the same.

As to operating differences between R-22 and 410a, I am not sure what your point is. If designing refrigerant piping from scratch, the more critical issues are pressure drop, velocity, oil entrainment, noise, etc. For example, liquid lines from the condenser to the receiver should be 100 fpm or less to ensure proper flow without liquid backup.

In general, refrigerant lines are sized as small as possible for cost reasons. Too small results in excessive pressure drop and in liquid lines can cause the refrigerant to flash, resulting in the expansion valve not operating properly. There are many additional factors in correctly sizing refrigerant piping, which is why I will always specify the manufacturer's piping to be provided. If I am spec'g, and designing, refrigerant piping for a commercial or institutional system, this will take me anywhere from an hour to the better part of a day or more, based on complexity.

But if the "professional" that installed your unit provided the same detailed system analysis in sizing and installing your piping, good for him. But in many cases, installers of residential HVAC equipment may have minimal experience (if any) in refrigeration theory, and are essentially inserting tab A into slot B. If you are fortunate enough to have someone like ricairmedic (a frequent poster on this site) handle your install, you will be well served. For most people, getting the heat pump/condensing unit, indoor unit and lineset, controls, etc. from a single source will always be the best choice.

The biggest single piece of advice I could offer would be to evacuate the system, regardless if pre-charged, to a deep vacuum (close to -30 inches) and hold for several hours before returning the refrigerant to the system. This will give you the best chance of avoiding start-up problems. Too many times I have seen inadequate pumps or too short times for this important step.

In the end rlitman, if you are pleased with your system, I am happy for you. Just wanted to share my experience for others, not get into a disagreement.

As always, offered only as opinion