How to air condition a FROG (finished room over garage)

[target2019]

FROG has two ducts. Do we know for certain that one duct is a return?

The duct or vent booster could help significantly. There are some that sit on a floor vent, and come on automatically when air flow is sensed. Otherwise you need to install inline and find power for it.
A transom door at foot of stairs would help a lot. May be called a folding door.
Attic fan is a must, assuming there is attic space.

[NW-Bound]

Quote:

Originally Posted by Amethyst #2 insisted that 9000 Btuh was better for the room than 12000 Btuh, because the larger unit would cool the room faster, which would cause more condensation and thus encourage mold! It sounded goofy, although the guy seemed like a straight shooter otherwise.

I saw this just now, and do not understand this.

It is not possible to cool without causing condensation, besides dehumidifying is also desirable. Here in the arid Southwest, I put a bucket under the drain line out of curiosity and catch more than 1 gallon a day.

In humid places, people often complain of mold growing in AC. I saw gross videos on Youtube. I don't know how it can be prevented.

PS. A booster fan in the existing duct is a possible low-cost remedy, if the main AC is sufficiently sized to handle the load. If it runs all the time now, then it's too small. If it turns off even in the midday, then it has enough capacity.

My single 5-ton AC runs nearly continuously without turning off in the hottest day of summer. I am glad to supplement it with a minisplit to the downstairs, because we do not use the 5 rooms upstairs much other than my electronic hobby room. I am able to raise the thermostat and save quite a bit of money. I could perhaps turn it off altogether, and let the upstairs get to more than 100F.

[NW-Bound]

Out of curiosity, I just checked humidity in several places as of this writing.

Phoenix: 63F dew point (we have entered the rain or monsoon season which starts in late summer)
Fort Lauderdale: 75F dew point
New Orleans: 79F dew point
Los Angeles: 59F dew point

I have measured the air blown out of the AC as cool as 55F. That explains the condensation I saw and described earlier.

I went out to look at the drip line. The water is coming out at a rate of almost 2 drops/second!

[Just_Steve]

Quote:

Originally Posted by Amethyst What does that entail? '

A zone control panel, a zone damper and a thermostat.

[samclem]

Step one is to do a heat load calculation for the FROG. If the folks who came out didn't do one (They might call it a "Manual J calculation"), you can do it yourself in just a few minutes. I like this calculator: HVAC Load Calculation - Maunualj - Whole House Loadcalc

Don't overlook that garage underneath--it could add a lot to the heat load of the FROG, especially if there's no insulation under the floor of the FROG.

We haven't talked about heat-- is the present system for the house doing an adequate job of keeping the FROG comfortable in the winter?

Quote:

Originally Posted by target2019 FROG has two ducts. Do we know for certain that one duct is a return?

Yes. If there's no return air (through a duct, through an undercut door, through a grill in the door, etc), then neither the heating nor cooling will be effective.

Before even considering using your present HVAC system, you'd need to know if the existing system has sufficient capacity, which is another set of calculations (or, you could base it on experience if you know the duty cycle of the AC system on your very hottest days. If it is running continuously, then it can't handle the additional load of the FROG). To make the temps in the FROG right, you'd need to add a separate zone to your present system IF it has sufficient capacity (so a separate thermostat, mechanical dampers, etc). It's still a compromise, and your system will be running at times when it otherwise wouldn't need to. On the whole--I wouldn't bother with that. I'd just get new equipment.

To restate some already said stuff, you have 5 approaches available:
1) Integrate the FROG into your existing HVAC (heating and cooling) system ductwork. For reasons above, I wouldn't do that.

2) Window AC unit for the FROG. These can be installed in a window OR a newly framed opening in an existing exterior wall (if the FROG has one--if it is all hip roof overhead, then you don't have this option). Cutting a new opening (vs using a window) means you don't lose any of the existing light, and you can mount the unit fairly high (which is best for cooling). Yes, you can buy a special unit designed for wall mounting, but a mass-market window unit will work just as well and will be less expensive. If you don't need to heat the FROG, this is a very inexpensive way to go, and the efficiency isn't bad. As stated--when the unit crumps out in a decade or so, you go get another one and you are done. Very simple. It will be a bit noisier than a minisplit, but it might not be a problem.
3) Minisplit: A deluxe answer and probably the answer most likely in an upscale home. When any part of it needs fixing, there will be a pricey service call. More efficient than a window unit, but the payback in utlity cost would for the minisplit would probably exceed the life of the equipment.

4) Minisplit with heat pump: Like Option 3, but with heat. More $$.
5) Window unit with heat: Like Option 2, but with a built-in heater. These are typically electrical resistance heaters ("heat strips"), so they are expensive to run. If your existing ductwork does the heating job, but not entirely well, this could be an option. Also, if you just need to heat for a month per year, or several hours per day, this might be fine.

You could also use a through-the-wall PTAC unit--which has cooling and heat-pump heating in one piece of equipment. These are common in motels, and cost less than $1000 for the equipment. Look for a quiet one. Examples:https://www.alpinehomeair.com/viewca...categoryID=248

A FROG can be some really useful space. We had one when we lived in NC, and DW and I spent a lot of time there--puttering around on our projects, etc.

[Amethyst]

yes, it does run like crazy when it's hot. The original owners had this one installed - it's not the original system. The system did pass inspection, but it's hard to know until you really live there. The house is somewhat upscale, but I think their priorities were elsewhere.

Quote:

Originally Posted by samclem If it is running continuously, then it can't handle the additional load of the FROG). 2) Window AC unit for the FROG. These can be installed in a window OR a newly framed opening in an existing exterior wall (if the FROG has one--if it is all hip roof overhead, then you don't have this option). >>Roof is a cement tile hip roof - a very hippy one, ha. I don't think there is any wood framing in the walls (all CBS with stucco on outside and drywall inside) but I could be wrong, so it's worth checking out. You could also use a through-the-wall PTAC unit--which has cooling and heat-pump heating in one piece of equipment. These are common in motels, and cost less than $1000 for the equipment. Look for a quiet one. >>Any time we've stayed in a motel, the unit has been very noisy indeed. Trying to avoid that! The contractors claimed they have mini-splits in their own homes and that they are very quiet. But I haven't been in their homes, so how do I judge? Examples:https://www.alpinehomeair.com/viewca...categoryID=248

[NW-Bound]

If the existing AC does not have enough capacity, then the minisplit is the only option.

A PTAC requires knocking out a huge rectangular hole, and Amethyst already said the walls are masonry. There's also no window, and there goes the windows AC option.

The refrigerant lines require a hole around 1.5" in the wall. They are actually smaller than that, but the bundle is usually covered in insulation foam of that diameter.

[samclem]

Quote:

Originally Posted by Amethyst yes, it does run like crazy when it's hot. The original owners had this one installed - it's not the original system. The system did pass inspection, but it's hard to know until you really live there.

That's actually a good thing--you've apparently got an AC system that is sized right for your home. It probably does a good job of keeping your indoor humidity low, something that oversized AC systems typically aren't good at.

Quote:

Originally Posted by NW-Bound If the existing AC does not have enough capacity, then the minisplit is the only option.

Yep, and it may be a good one. Doing the heat load calculation can help you decide on the system size--get what you need, but not larger.

As a bonus, having a completely separate AC system will give you a spot to hunker down for a day or so if when your main AC unit crumps out. Pretty nice, and could save you big bucks over having to go with the overpriced "we can install a replacement right now" option.

[Amethyst]

As always, I so appreciate everyone's thoughtful, helpful comments. Please keep them coming - I will review and digest before talking to any more contractors.

I did find, and talk to, the contractor who installed the current a/c system for the previous owner. I explained that the system was struggling, and asked (politely) how he determines the size of the system to install. He said, "As I recall, we just replaced the system that was already there." In addition, he remembered the previous owner complaining about heat in the Frog. He provided an estimate for a mini-split, and never heard back.

His attitude about sizing doesn't seem terribly professional, does it? Then again, it's possible he did not bother to analyze and size the system, b/c the previous owner just directed him to "replace what's there."

[Amethyst]

Oh, my. That heat load calculator asks for a lot of info that we can't lay our hands on. Especially insulation - except for the attic, which has about 16-18" of loose insulation, there's no telling what's in the walls, floors, ceilings. Even the garage under the Frog is drywalled.

Quote:

Originally Posted by samclem Yep, and it may be a good one. Doing the heat load calculation can help you decide on the system size--get what you need, but not larger.

[Amethyst]

I wonder - would some photos of the Frog and the entrance to it be helpful?

[samclem]

Quote:

Originally Posted by Amethyst His attitude about sizing doesn't seem terribly professional, does it? Then again, it's possible he did not bother to analyze and size the system, b/c the previous owner just directed him to "replace what's there."

This attitude is very typical. They'll just use a rule of thumb, maybe based on little more than the SF of the floor. Typically, the result is units that are too big for the requirement (additional capacity doesn't cost them very much--a 3 ton unit and a 4 ton unit may only be a few hundred dollars different), and reduces the chances of a callback. Oversize units keep the spaces cool enough, but don't remove sufficient moisture--it's easier to tell the client that all is well if the house is just constantly clammy, you can't tell them that things are fine if the temperature won't get down to the set point.

Quote:

Originally Posted by Amethyst Oh, my. That heat load calculator asks for a lot of info that we can't lay our hands on. Especially insulation - except for the attic, which has about 16-18" of loose insulation, there's no telling what's in the walls, floors, ceilings. Even the garage under the Frog is drywalled.

And knowing the insulation level is important--you can be sure the guys who gave you the estimate never checked it.
I'm glad the garage ceiling has drywall, that's now required between a garage and habitable areas (it gives you time to get out in case of a garage fire).

If you want to go to the trouble, you can often tell about the insulation by looking beside the electrical outlet boxes. Turn off the power, remove the cover, and (sometimes) there will be a gap between the drywall and the box. You may see fiberglass there. You can also insert a bit of coathangar wire bent into a hook on the end into that gap and try to snag some insulation, to see what kind there is (again-- circuit breaker OFF). Use the same wire to see how deep the walls cavities are. If the cavities are 3.5" deep (2x4 walls) and the insulation is fiberglass, then it is an R13 wall (it >might< have additional insulation as sheathing). Between the garage and the FROG, you may be able to get a peek into the cavity to tell if it is insulated by removing a light fixture in the garage, or by checking around any receptacles in the ceiling (usually used for garage door openers). Hopefully, they did insulate the garage ceiling.

If you've got a hip roof over the FROG, I'm guessing you have knee walls (about 42" high) all around the room, likely with a small door you can open to use the area behind for storage. If so, you can tell everything you need to know about their heat loss by going into that back space and seeing how the knee walls are insulated.

If all of this is more trouble than you want to go to, you could ask the next person who comes out to do an actual heat load ("Manual J") calculation for that room--for heating and for cooling. If they charge you a couple of hundred dollars and they actually investigate all the factors (insulation, shading by trees, window types, etc) it will be probably be well worth the money. IMO, a reputable HVAC company would do it for free as part of the bid--how else can they know what type of equipment you need? They can't.

[NW-Bound]

Quote:

>>Any time we've stayed in a motel, the unit has been very noisy indeed. Trying to avoid that! The contractors claimed they have mini-splits in their own homes and that they are very quiet. But I haven't been in their homes, so how do I judge?

PTACs and large window ACs tend to be quite noisier than mini-splits because of a very simple reason: the mini-splits have their compressors and the exterior fans remotely located. In addition, the interior units or inside-air handlers universally use a long horizontal squirrel cage fan, which is a lot quieter. That's how they all have a longish shape.

Plus, one has to remember that in contrast to old AC units that wake you up when they turn on/off, the mini-splits slow down once the interior has been cooled down, and run very quietly at night because it is not as hot at night.

The key is they have "inverter technology" that can continuously vary the speed of the motor, much like how the motors in electric cars work. They don't run at a single speed like old ACs, nor at only 3 speeds like ceiling fans. The electronically controlled speed is continuously variable over the motor operating range.

The old motors run like a car driven by a driver with a lead foot. Full acceleration to the next traffic light, then stop. Then, full acceleration again. In engineering, we call it "bang-bang control" for systems that control their outputs by cycling on and off. That was the only way we could modulate anything then, by using an on/off switch.

Practically all current minisplits on the market use inverter motors. I would be surprised to see any old types being sold, but I guess some old stocks may still exist.

See: https://www.inventorairconditioner.c...r-conditioners.

The curious may want to read about the "bang-bang control" devices that surround us: https://en.wikipedia.org/wiki/Bang%E2%80%93bang_control.

[NW-Bound]

About the noise, my 18,000-BTU/hr Pioneer mini-split makes much less noise when running at its top speed than my 16' pedestal floor fan running at its lowest speed, and moves a lot of air.

Nuf' said.

PS. The outdoor unit also makes less noise than the normal AC of the same capacity. They really know how to make them better.

Do they last? Time will tell.

[travelover]

Quote:

Originally Posted by samclem This attitude is very typical. They'll just use a rule of thumb, maybe based on little more than the SF of the floor. Typically, the result is units that are too big for the requirement (additional capacity doesn't cost them very much--a 3 ton unit and a 4 ton unit may only be a few hundred dollars different), and reduces the chances of a callback. Oversize units keep the spaces cool enough, but don't remove sufficient moisture--it's easier to tell the client that all is well if the house is just constantly clammy, you can't tell them that things are fine if the temperature won't get down to the set point...........

I know this is true for typical AC systems, but NW seems to feel that the mini splits are variable speed, so the issue of over sizing might not be so critical. In that case I'd go for 12,000 btu.


I still think the installation labor quote was excessive.

[imoldernu]

https://www.walmart.com/ip/GE-8-000-...d9&athena=true

My solution for my 400s.f. all windowed addaroom @ woodhaven.

[samclem]

Quote:

Originally Posted by travelover I know this is true for typical AC systems, but NW seems to feel that the mini splits are variable speed, so the issue of over sizing might not be so critical. In that case I'd go for 12,000 btu.

Yes, I agree, if the compressor itself is variable speed. In that case, a large unit would be fine (it would cool the space more quickly when you started using the FROG and the set point was well below the temp in the room). Also, if it is a heat pump it is possible that a larger capacity is driven by heating rather than cooling requirements.

[NW-Bound]

Quote:

Originally Posted by travelover I know this is true for typical AC systems, but NW seems to feel that the mini splits are variable speed, so the issue of over sizing might not be so critical. In that case I'd go for 12,000 btu. I still think the installation labor quote was excessive.

I am enjoying one right now, and have been monitoring its operation.

The indoor air handler fan, the compressor, and the outdoor fan all have their speed varied with the load. It is very noticeable. I can just raise or lower the temperature setting to see the unit ramping up/down as it needs.

Right now, the lowest temperature of the day at 5AM before sunrise is still about 90F and above the house interior temperature. This means the unit can never be off, and indeed runs 24 hrs a day, albeit at a very low speed in the morning.

I have observed the power drawn of this 18,000 BTU/hr unit being the max at 1.4 kW in midday to 300W in the morning. No "bang-bang control". It's just beautiful.

When it gets cooler in a couple of months, I expect to see the outdoor fan and compressor completely stop in the morning, while the indoor fan runs at a very low speed to circulate the air.

This unit will not switch itself between Heat and Cool modes. I don't think that is desirable anyway.

PS. Because I did the installation myself and did not ask for any quote, I do not know what the normal charge is. In my case, it involves quite a bit of work to run the 33-ft refrigerant lines through the attic.

[Amethyst]

We are in southeastern Florida, where it can get aaaall the way down into the 50's in midwinter. I don't think we need to worry overmuch about heating.

Quote:

Originally Posted by samclem Yes, I agree, if the compressor itself is variable speed. In that case, a large unit would be fine (it would cool the space more quickly when you started using the FROG and the set point was well below the temp in the room). Also, if it is a heat pump it is possible that a larger capacity is driven by heating rather than cooling requirements.

[Moemg]

I would also look into shades for the skylights .