Comments on: Navigating the Twilight Zone: The Hidden Flaw in a Zoned Duct System

By: Ray Austin

Ray Austin — Fri, 05 Sep 2014 16:53:50 +0000

Ok I decided to do some
Ok I decided to do some checking on
this VRF vs VRV subject… this may
shed some light. LOL. (who knew?)

What is the difference between VRF & VRV?

They are essentially the same thing, EXCEPT the term VRV is copyrighted by Daikin. for example a system by Daikin may be called a VRV, but a similar system made by Fujitsu is a VRF.

VRV = Variable Refrigerant Volume, VRF = Variable Refrigerant Flow. http://www.refrigeration-engineer.com/fo… VRF or Variable Refrigerant Flow is the technology being applied by manufacturer’s such as Samsung, Hitachi, Daikin, etc.

VRV is the trade name for Daikin’s VRF product lines. Hitachi uses Set Free, while Mitsubishi uses Mr. Slim. These are trade names for VRF the uses inverter compressors.

Samsung uses DVM, Midea uses MDV, while Trane uses TVR. These VRF technologies however use Digital Scroll Compressors which is a new technology in the market.http://www.refrigeration-engineer.com/fo…
Source:
http://www.refrigeration-engineer.com/fo… http://www.refrigeration-engineer.com/fo…

By: Ray Austin

Ray Austin — Fri, 05 Sep 2014 16:19:43 +0000

Mr. Butler, yes it's true
Mr. Butler, yes it's true there are so many different ways of doing things on the mini split side it's enough to make one's head spin to try to keep it all straight. (eyes crossed)

VRF comes from "variable refrigerant flow"... In my opinion this is a short descript method of telling you the compressor is likely variable speed and from what I could tell when I initially looked at this stuff is that VRF is usually used in a mini split zoned system.

However, you will find differences from manufacturer to manufacturer in the mini split realm. In fact there is another flavor of the VRF type system called VRV. In my opinion VRV is more likely for a commercial type set up, although some large McMansions could deploy this kind of beast if they wanted to. I really don't know specifically what makes one system a VRF a VRV or just a multi zoned mini split, do you? (Unless the manufacturer tells me what it is.)

When I was talking about VRF, it was to discuss the hurdles and cons of that particular set up as a whole and not necessarily include the multitude of ways someone could go via other methods of using mini-split type set ups.

If anything your point is important in regards to the complexity as well as the non-standard ways of doing things via the mini split method. Meaning that if you choose one type mini-split method over another you will most likely be stuck with that choice or spend more money each time you decide to diverge from one manufacturer's way of doing things.

With that said... very good point to bring up David.

By: David Butler

David Butler — Fri, 05 Sep 2014 11:23:08 +0000

@Ray, although it doesn't
@Ray, although it doesn't change the thrust of your commentary on VRF, just as a point of clarification, not all multi-split systems are considered VRF, at least not according to the nomenclature used by manufacturers.

In general, commercial multi-splits are considered VRF and residential multi-splits are not.

Some examples: Mitsubishi City-Multi line is VRF, whereas Mr. Slim MXZ in not. Likewise, LG Multi V is VRF but Multi-F is not. And the Fujitsu J series is VRF but their HFI multi-split line is not. (Multi-F and HFI are functionally similiar to MXZ.) Commercial VRF systems, sometimes used in high end residential, employ an active refrigerant management system. Some models can even heat and cool simultaneously by exchanging heat between zones ("heat recovery").

By: Ray Austin

Ray Austin — Thu, 04 Sep 2014 21:26:07 +0000

High end equipment is only
High end equipment is only made in
2 ton, 3 ton, 4 ton & 5 ton
(residential market.)

In some cases they may not even make
a 5 ton system and may require you
to twin the furnaces and put in
multiple systems to accomplish the
larger loads that a 5 ton system would
require.

The sizing argument is fraught with
danger... and a Manual J is easily
skewed if you just make up or guess
at insulation levels.

Where is Superman with his x-ray
vision when you need him?

Manual J's just as much as negating
a bypass doesn't compensate for poor
design.

Give a salesman a manual J and a ruler
and what do you think you're gonna get?

That's the skinny version of this
serious sizing problem....

By: John Phillip Brown

John Phillip Brown — Thu, 04 Sep 2014 18:52:19 +0000

Understood...HVAC problems
Understood...HVAC problems come in all flavors.

Thanks for the discussion.

By: Allison Bailes

Allison Bailes — Thu, 04 Sep 2014 18:44:04 +0000

John B.:
John B.: Just to clarify, the photo above is not my house. I used that photo simply to illustrate what a bypass duct looks like. My personal HVAC system certainly has problems, as I confessed yesterday, but bad zoning isn't one of them.

By: John Phillip Brown

John Phillip Brown — Thu, 04 Sep 2014 18:03:44 +0000

Thanks for the clarification
Thanks for the clarification but I still can't see it.

I highly recommend an electronic bypass damper, regardless of the duct orientation. They are vastly superior to any mechanical bypass damper.

In any case, this bypass duct lacks a balancing damper and will therefore become the path of least resistance, when one or more zone dampers close down.

That condition will allow a higher airflow thru the bypass duct, than was intended, which will adversely affect the Delta P and the Delta T of your system.

No wonder you were disappointed with the zone system.

JPB

By: Allison Bailes

Allison Bailes — Thu, 04 Sep 2014 17:49:04 +0000

John B.:
John B.: The perspective may be fooling you here because that section of the bypass duct is horizontal. It goes straight back into the return plenum. The only vertical section on the bypass is the short piece that comes down out of the supply plenum.

Thanks for the info and the link, which I've made clickable here.

By: John Phillip Brown

John Phillip Brown — Thu, 04 Sep 2014 17:42:39 +0000

Mr. Bailes,
Mr. Bailes,

It's hard to see this counter weight bypass damper, but if it is to the right of the red arrow, then it has been installed on a vertical duct run and that will never work!

I don't know why Installers keep doing this. A counter weight bypass damper (which has a limited control range anyway) is designed for a level horizontal installation only.

An electronic (motorized) bypass damper must be used on a vertical bypass duct! In addition, any bypass duct MUST have a volume control hand damper in series (downstream) of the regulating bypass damper.

This allows the Installer to BALANCE the bypass duct and restrict the bypass volume to the desired value! Without the hand damper and proper balancing, the bypass duct will become the path of least resistance!

Installations like these, are why the bypass has such a bad reputation.

The link below will be helpful.

http://www.ewccontrols.com/acrobat/090376a0169.pdf

Best Regards.

By: Allison Bailes

Allison Bailes — Thu, 04 Sep 2014 17:03:47 +0000
Jason: The
Jason: The bypass duct in the photo above does have a damper. It's hard to see here, but the arm and weight are hanging down just to the right of the red arrow.