Saw a few minutes of TOH today, and they were talking about a high velocity a/c system for the project house. The ducts are smaller. Other than that I don’t know anything about it. What are the advantages & disadvanteages?
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Replies
Ours works nice, it takes a lot of humidity out of the air without turning the thermostat way down.
The main disadvantage for me is not that many people around here like to service the unit. The pressures for the unit are different from conventional units and since not many high velocity units are sold, they don't fully understand how they work.
What about a brand name ... ?
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt
Two I know about are Spacepak and Unico. Used to be another around but I forget their name. I'll do a quick search.
System is a Unico, uses a ruud compressor.
works great for remods, no large trunk lines
You still could need a decent trunk line--our Unico system has a 9" round--but the branches to the vents are 2" + the insulation, and that's nice.
I've wired a few of them. They all were hooked up to heat pumps and one had an inline electric heating unit in the system. They all were installed in old homes that had no central AC and steam heat. In the one with the electric in-line heat, the steam system was removed from the house.
The big advantage I see is the ability to install central air in an old house without butchering the place in order to run ductwork. And without having to incorporate large duct openings into the finish of the old house.
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I've heard these systems are noisy because of the reduced duct size. Is that right? What does one of these machines cost? Anybody have a ballpark figure?
They tend to "whistle" at a high pitch, and are priced about the same as conventional systems if not higher.
They shouldn't be noisy if people have installed the manufacturer's sound attentuators at each outlet and install the right # of outlets, etc.
Not at all in my experience. And certainly no high pitched whistle.
I installed a Unico system in my home; actually two of them, one for third floor, one for second floor. It think that they probably are a bit more expensive than the "standard" big-duct systems, but they are easy to do, and particularly in a retrofit situation as mine was.
It uses any manufacturer's compressor of the right size for the heat load.
The air-handler comes in multiple pieces so that you can pass them up through the ceiling joists without cutting any, and assemble the whole unit in the attic (if that's where you're putting it). The air handler consists of the input plenum that collects the return air lines (standard size ducts required), the evaporator, and the blower, at a minimum.
It does require a large size duct coming off the blower: 9" diameter in my case. I used steel rather than the fiberglass sort of stuff because I had a long run and needed to have minimum friction losses in that plenum. I installed a loop plenum in the attic for each of the two floors, and fed the 2" lines off that.
System runs great, and had a real test this summer with our extraordinary heat this year (New Jersey). You can hear the air moving, but I don't think it's much different from a standard system in that regard. I'm very pleased with it and so is DW.
BTW: I had never done an A/C system before. I found the heat load calculation software online for a nominal charge for a month's use. Took the calculations to my local Unico distributor, and he verified that I had it about right. He also put me into his contractor's education class, which was great. The Unico manuals are very good, and it's easy to figure out what parts you need.
The only thing that I had to hire someone for was to silver solder the lines between compressor and evaporator, and charge the system. I have never done silver-soldering, and you need a license for the refrigerant, though I now understand that I could have easily enough gotten a "homeowner" license to do this one system.
This is very helpful, Bob. Thanks. I'm like you, never done anything with A/C. Couple of questions. You say you had to install a standard return. Did you just run this from a central location?I'm thinking about getting rid of my forced air and moving to a radiant system. Sounds like I could send the old furnace to my rental and use the compressor I have with the Unico. Is that right? That'd be nice.
ndege:
Most returns, as I underwstand it from the training session, are run from a central location (perhaps the hallway). It then works by sucking the return air under doors from the bedrooms, etc. However, I put separate returns in each room or in groups of rooms: for example, the master bedroom has an attached dressing room and bathroom, so i used one return for those three rooms together. A lot of this will depend on where you can get access, as the returns are from 6" diameter to 18" or so (I forget exactly). The one thing that they caution you about in using these high-velocity systems is to make sure that you provide a large return air path so that the air handler isn't starved for air.
On the third floor, i used a single return from the hallway for everything except the bathroom. I then put "feedthroughs" from each room to the hallway. These were just back-to-back grills on each side of the walls separating the hall from each room, so it may suck a little bit of air up through the wall cavity that's between the grills, but with my leaky old 1883 house, that is going to be a very small percentage loss in the system.
Yes, as long as the compressor is properly sized for the load, there's no reaon not to re-use it. For me, it would depend on how many years of service it had already given, and whether it still uses the right refrigerant --- as you perhaps know, the refrigerants that are now permitted are somewhat different, so i don't know if there would be compatibility problems or not.
Bob
I don't think our high velocity system is any louder than a conventional system. There is no whistle from our system and it is a bit quieter than some conventional systems.
I can't remember the exact prices but the main components are the air handler, compressor and ductwork. The ducts were not inexpensive. I installed the system so my costs were for materials. The material costs could have been between 4-6k.
Thanks all. I've talked with several HVAC guys who were all pretty negative about the Unico--that's if you can get their attention at all.
that's if you can get their attention at all.
You talking about getting Unico's attention? Great. I sent them an email asking for more info.
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt
Here in Baltimore, I could not get anyone to sell me the Unico system. I did the load balance and had all the part numbers, but the distributor wanted an HVAC lic. even though I was not purchasing a compressor nor freon. Still have the window shakers until I find another solution. All the local install contractors don't want to do Unico, if they even return your call.MY OH
I live near Baltimore and found several contractors who can install Unico. The best so far is Carroll Independent - in the planning they are very thorough and think Unico is a great system for old homes or retro installations. HVAC is still a tightly controlled product in our area - your best bet is to find someone who does HVAC both as their job and on the side. You can use their expertise and your labor to cut costs.
No, I was talking about HVAC contractors.
Many HVAC people I've met are tied to a particular system, and don't look so favorably on competing systems. It's almost like going to a Dodge dealer looking for a Blazer. Think they'll try to sell you a Durango instead?Why didn't they like Unico? Price? Service? Doesn't work? Are their objections legit or be/c it's not in their business interests?Call Unico and ask for a local rep.
Is the air still at a high velocity when it enters the room or does the baffle/diffusers create a result similar to a conventional ducted system?I seem to recall the manufacturers suggesting putting the duct in an out of the way spot to minimize drafts. So if you walk under it will it be obnoxious? Will it move drapes or curtains? Blow a newspaper out of your hands? You get the idea.eric
It's high velocity out of the duct, compared to a traditional ducted system. Mine are all directed where they won't blow on a person, so we really don't pay attention to the effect they have on us, be/c there is none. And I haven't found them to be draft-inducing in any fashion. A leaky window causes a noticeable draft, but these do not. The air flow is about like you'd use to blow out a candle, maybe less. But, again, it is such that you neither hear nor feel it in any significant way.
Edited 11/19/2005 8:48 pm ET by CloudHidden
They didn't like Unico because of the small ducts--said they would be loud. See, I think they have no experience with it but can't say so. It would somehow chip away at their sense of authority to say, "I've never installed one of those systems. I'll look into it." The lackluster response I got was from several contractors when I asked about the small-size duct systems, not the Unico system particularly.
I suggest that if you want more/better info that you call Unico directly. They have been very helpful to me over the phone. They can probably refer you to a local distributor who will be happy to help you with purchasing the equipment.
Bob Chapman
>They didn't like Unico because of the small ducts--said they would be loud.OK, thanks. I can unequivocally say they are wrong. But the best thing is to find from Unico a local contractor and see/hear for yourself. Maybe my ears are damaged from too much rock 'n' roll! <G>