Residential High Velocity A/C systems

[CptHk]

Looking for opinions on the residential style high velocity AC systems. Typically 2000 FPM fed through 2" and 3" flexible ducts.

Are these systems noisy compared to either the mini split VRV systems or typical low velocity hard ducted systems?

Due to high velocity, is static pressure so high as to make the fan energy significantly more than low velocity residential systems?

 

[IRstuff]

The ducts aren't necessarily the noise makers. In my house, it's the registers.

TTFN

FAQ731-376

 

[GMcD]

Noisy: yes, they can be if attention isn't paid to keeping duct runs smooth and straight, and the exact right type of air terminal outlet must be used.

Fan energy- yes- that can be a high percentage of system energy use.

These systems rely on jet-mixing high velocity, but very cold (and dehumidified) air, with room air to create mixed conditions. In some climates where indoor humidity may be high, the air terminals (small plastic jet nozzles) may get condensation on them from the entrainment of room air in the jet/mixing stream.

 

[Wareagl487]

I've had architects fresh from a trade show ask my thoughts on the system. My response has been that I have no design experience with this type of system but my inicial reservations are:

Higher equipment cost - due to increased statics preventing the majority of residential/light commercial equipment manufactures from meeting the spec.

Higher energy cost - from larger H.P. airhandlers to meet S.P. requirements.

On the plus side I would think it would be a less installation cost.

But like I said, I have no priors with this system.

Very interested in opinions.

Andy W.

 

[RossABQ]

What is the driver for using these systems? I'd have to assume it's to address an architectural problem.

 

[CptHk]

RossABQ,

Architectural, Yes. Old big house to be used for offices for college. I'm most concerned about lack of zoning. But that will be brought up soon with the client. I wanted to find out about the rest of the potential issues.

Thanks all for your input so far.

 

[willard3]

If you have a high and constant requirement for heating/cooling and OA (as in hospitals) I think they are a great system.

Not many people make them anymore.

The fan pressure required is high and they can be noisy if improperly designed/installed.

 

[UtilityLouie]

I actually installed one of these systems in my home. I have hot water heat and a walk out ranch style home with most of the lower area finished. We had two options: conventional fan coil with large ductwork, new soffits and diffusers OR the high velocity system.

The system is noticeable when it is on, but it is not a mechanical noise, it is a "white" noise. In a new system install, I'd be a little hesistant to use it but I've heard furnace systems just as loud. The only difference is lower hp and static with a furnace - not necessarily noise.

The lower humidity levels in our house due to this system is noticeable and this atmosphere is more comfortable in my opinion.

I've always wondered about their possible application in a new home with in-floor radiant heat. That seems like a good match - clean floor lines.

Oh - one other thing about these systems - the jet diffusers are not obtrusive. You don't even notice them. They usually have a paintable variety and if you use them, you can make them essentially disappear.

 

[GuyH]

I designed and installed one for my parents. They are more energy efficient than a standard heat pump system. Because the high velocity fan pushes air through 2 inch vents it causes the air to sit on the cooling coil longer thereby removing more moisture which in turn means you can have a higher temp setting on your t-stat. When you are looking for these systems and people to install/design them you should do some research as well. 90% of the hvac people do not understand the high velocity systems. And no one runs a manual j on the house. Be forewarned.
As far as noise, research the manufacturer. Those who require special vent reductions or special sizing for long runs will give you more noise.

 

[gepman]

After reading the above posts it sounds as if these high velocity cooling systems rely on smaller volumes of colder air to accomplish approximately the same refrigeration effect.

The lower humidty due to the colder air sounds as if it has a comfort advantage in humid climates. I don't see the energy efficiency benefits that GuyH mentions. The fan energy may be a wash since it has a smaller volume but at a higher pressure than standard systems. I would expect the compressor energy to be higher however since the suction pressure (or temperature) should be lower than a standard system and it will have a higher latent heat load with approximately the same net Btu/hr.

 

[lownox]

These systems have no efficiency benefit. In fact, manufacturers were, not to long ago, trying to get their own category for EER/SEER. I don't know the outcome though, but I used to work with some guys from SpacePak. With the main difference being the motor engergy, these systems just can't be as efficient as todays typical split system AC's.

Duct systems are smaller and will fit inside 2X4 walls and such, so retrofitting old homes is a big market for them.

Blah Blah Blah... you probably already know all this.