High Velocity Systems

Jed_2

Branch supply tubing is the same, but fractional balancing does come into play with orifices if CFM load distribution and static pressure are to be right. There is site engineering in that.

Jed

Bob Forand

High Velocity systems

Has anyone received a quote lately on high velocity systems versus conventional air ? There have been other posts recently that claim that high velocity is expensive compared to conventional systems. Times are a changing folks...High velocity systems are only approx 25% or so higher. With steel gone crazy..High velocity isn't that far off any longer.

Christian Egli_2

And he huffed and he puffed, the big bad wolf

But that's only half the story and half the cost.

Regardless of up front cost, a high velocity system is much more expensive to operate than a conventional one. Unlike steam, air does not move neither free nor cheap.

Since we plan on using these systems for ever and ever, the extra operation cost may dwarf everything else.

Unless the building is really so cramped there is no space for anything else, then the high velocity is the thing you need.

Ductless systems present neither the ducting problem nor the big air moving cost. There are even combined AC and heat pump split units that hide behind your picture frame. Combine this with your steam and radiant muscle heat and you've got yourself a highly adaptable comfort system.

High velocity/pressure whole building systems were the rage in the seventies, and they turned out to be energy hogs.

I think the big bonus of high velocity piping is that it may be less cozy for the dust bunnies to settle in, but only less.

Brad White_57

Different view

The high pressure systems of the seventies were indeed energy hogs to the extent that they used/required 6 or more inches of pressure external to the air handling units and up to 10 inches across the fan to cover coils, dampers and filters.

Unico/SpacePak type systems characteristically move about half the air at about twice the pressure (ring ducts keep this lower) so the air transport costs practically wash out as equal.

The refrigerant side is the same tonnage, sized the same over less total mass-flow.

Given it is running at colder temperatures (about 40F off the evaporator versus 52 to 55F) I will concede the inefficiency to achieve that versus lift.

But no real comparison to the high pressure single and dual duct systems prevalent in the 1950's to the (early) 1980's.

I would welcome more opinions on actual operating and seasonal cost experience of course, from users and installers. I just did not see a linear comparison to the big old systems, that's all.

Ductless split systems? I agree, Christian. Different animal but more efficient especially on the air side of things. But ducted to ducted, low to high velocity? Closer than you think from the design perspective but I do not have empirical nor quantitative data to support that.

Respectfully,

Brad

Ted_9

a/c

this should be interesting.

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Mark Hunt

One other point

Brad, I agree with you.

BUT........(always one of those).......

High-V systems are marketed on smaller duct work. While the supply duct is indeed smaller, the return ducting is not. In 99.9% of the systems that I have seen installed by "competitors", only one central return existed.

How does one "balance" an entire home or building with one central return?? Can't be done.

High velocity companies only address one half of the system and totally ignore the other.

Simple physics. Steam guys should understand this better than anyone. The flow entering will equal the flow leaving.

So once a space is pressurized, the only way to get more air in is to overcome that pressure. Hyperbaric chamber anyone???

The opposite is true as well. If you place that central return in an "open" area like the family room with the fireplace and shut all of the doors to each room, the family room will go negative. More air being removed than the space has to give. Now let's put a fireplace in that room. Which way will the air in the chimney move?

If I trusted them, I would send this challenge to "Myth Busters".

The math is very simple as well. BTU/HR out replaced by BTU/HR in. I get xxx BTU/HR/CFM @ a delta T of X. It's that /CFM part that makes or breaks the system.

Perhaps Hi-V systems are marketed towards the hydronic guys for this reason?? Smaller duct and less of it??? Try this.... supply a baseboard with 3/4" and return it with 1/4". Or better yet, no return at all.......I'll wait....

Now I am sure that there are many contractors here that have installed systems with one central return and have "never had a complaint". Doesn't surprise me. I will never cease to be amazed at what people will grow accustomed to. But a ducted system requires no less "engineering" than a HW circulated system does.

BTW, the "scorched air" thing is infantile and snobbish. I, for one, am sick of it. But if one of you millionaire STRICTLY HW or steam guys want to chime in and tell the rest of America how to become as wealthy as you are, feel free. While you are at it, tell me how you address the IAQ of your customers home with your system. "RADIANT!!!! NO CONVECTION!!!!!" (Wipe nose on sleeve). "YOU DON'T NEED A HERMIDIFIER!!! I PUTTIN' IN RADIANT!!!!"

"ALERGEEZE?!?!?!? RADIANT CURES ALERGEEZE!"

Reminds me of the carpet-bagger in "The Outlaw Jose Wales".

"This, my friend, can cure most anything".

Okay........You drink it.......

Where was I, ah yes....

HI-V.....installed according to sound science, works very well.

HI-V installed to manufactueres instructions sucks. No wait....blows...uhhhhh........it's one of those or both.

Good luck.

Mark H







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Gordy

Bad Day ????

Geeze Mark, no winning lottery ticket today I have not seen anyone bost a millionare status from radiant heat around here. IAQ = ERV or HRV in a WELL designed radiant system. There are poorly designed FA systems, and poorly designed radiant systems....The carpet baggers are everywhere. Buyer BEWARE !

Gordy

Christian Egli_2

Those old pressure monsters scare me. $$

I should not have hinted the old high pressure system and new high velocity system were that closely related.

Thanks for pointing out the added qualities of the new high velocity systems as far as the piping goes. No matter what, I think it is really smart to think out the whole air flow problem and to provide for a nice efficient piping.

What if conventional piping were sized and shaped with the same care? Do you think the running costs would shift back solidly in favor of the conventional air handler? I don't have real numbers either.

Now that you got me thinking, I am wondering how this relates to the case of the counter intuitive low pressured steam flying at high velocity vs. the high pressure slowing it all down, except, as you point out, the mass flow rate is not kept through. But which is which. Got to go sleep over this one.

Thanks for making me pay attention to progress and for comforting me with my big bad wolf nightmares.

Mark Hunt

Well Gordy


Again from "The Outlaw Jose Wales".............

"I didn't surrender, but they took my horse and made him surrender......they got him pulling a cart in Kansas I bet."

Mark H

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Brad White_57

That was more of an \"and\" than a \"but\", Mark...

Good point on proper return versus BSR (big single return) too.

Whenever I specify HV, it is usually as a value engineering excercise so there must be a cost benefit in there or it would not come up. Then again the 'savings' on return ductwork may be part of that.

(Another topic you can quote me on: "Value Engineering is Neither")

chuck_6

Unico vs conventional AC

For what it's worth, we have a conventional AC system on our second floor and a Unico system on our first floor. I am much happier with the conventional system. I think the Unico people undersized us, and it is on for 10 minutes, off for 10 minutes. Needless to say it is not very helpful in paying the summer utility bills. Given a choice, I would stay with the conventional system.

Chuck

Gene_3

I have one

Unico that is

I had a hard time sizing because I have a raised ranch and only wanted to control humidity downstairs, I went with a 3ton for fear of oversizing which I think people tend to do with these, psychosamatic or something

I had the rep out because I have a high wall at the center for a cathedral ceiling because I really needed to know the throw--I needed 20ft, at a 15 ft ht I got it

I really needed to go with the small ducts a high velocity for my home, they are better as far as humidity control and aspiration, sizing, planning and install are all more critical with these

what I did was size it for upstairs and added 2 outlets one for one side and one for the other downstairs with a return in each center hallway

the downstairs is within 1-2* of up and humidity is controlled, my cycles are long and water pours out my condensate

it took me, by myself from sept- may to complete and $$$$$$$

Brad White_9

I am thinking that you were over-sized, Chuck

10 minute on-off cycles says over-sizing to me, not under-sized.

Long and steady operation would be the hallmark of nice, tight and proper sizing. If judiciously under-sized (art as much as science, say a 3 ton calculation design, maybe a 2.5 ton system) it is always trying to play "Catch-Up" and will dehumidify in the process. And Unico's (an others of the genre) do dehumidify well.

Suggest you check ways of tuning the unit, things short of changing out the condensing unit that Dr. Silberstein might know, as a way to get you into a longer operating cycle.

As I once mentioned in a similar thread, High V. systems do not turn over well, low mass flow means long times to recover sensible (temperature-based) comfort. Best left running; set-backs/set-ups are discouraged unless you can start the unit well in advance of occupancy.

My $0.02

Brad

Ted_13

The SEER ratings say it all

Check the SEER ratings of the system on hte ARI website. It is true that you do pay an energy penality to run hte system at a higher static pressure but the difference is not huge. The SEER ratings are based on 1000 hrs of operation. Do we have 1000 hrs of operation durring a typical Long Island summer? If not then the difference is less. What'ss the difference between a 12 SEER system and a 13 SEER system in New England as far as the electric bill is concerned? 10$-20$ a month? times 4 months= 40-80$ a year.

Ted_13

The SEER ratings say it all

Check the SEER ratings of the system on hte ARI website. It is true that you do pay an energy penality to run hte system at a higher static pressure but the difference is not huge. The SEER ratings are based on 1000 hrs of operation. Do we have 1000 hrs of operation durring a typical Long Island summer? If not then the difference is less. What'ss the difference between a 12 SEER system and a 13 SEER system in New England as far as the electric bill is concerned? 10$-20$ a month? times 4 months= 40-80$ a year.

Ted_13

Except that

It is true that many, maybe most High Velocity systems are installed with a single central return however if doors are normally shut cutting off the return location from other parts of the building it is recomended to split the return as you would with a conventional system. The facts are that you are moving just over 1/2 the air of a conventional system at a greater Delta T. The size of the return is the same as a conventional system for that air volume. If you want to compare it to steam then it is like putting the pressuretrol up to 5 PSI with a 1/2" riser and a 6" return line.

Ted_13

Delta T not the energy monger

The delta T is greater with High Velocity units because the air is in contact with the coil longer 6 rows verses 2. The energy difference belongs to the evap. blower motor maintaining 1-1/2" static pressure. I'm curious, what are your low velocity systems running for static pressure in cooling mode?

Ted_13

Sorry I can't stick with the thread

I hope the discusssion will continue till next week I would love to now the real difference between these 2 types of systems from an energy standpoint and clear up some of the misconseptions if I can, but I have to head to the Bahamas and set a hook in some wahoo's mouth

Brad White_9

Wahoo is a fish, right?

Not one of the locals?

Just checking, Ted.

Send a postcard from Margaritaville.

Plumdog_2

You are correct Sir

A Wahoo is indeed a fish, but a local may be a Yahoo. As in "slack-jawed Yahoo".

Brad White_58

Thanks, PlumDog

Can I pull your other leg or will that tip you over?

RianS

HV's

I understand there are some applications where hv's may be the only choice but we tend to stay away from them. I cant tell you how many times we had a new customer call and say there system blows snow flakes out of the supply register or there is water dripping from the supply register. We all know in hydronics that the lower the water temp. with longer cycles is the most efficient way to heat. I cant help but believe the same is true for cooling. High temp. drop and high pressure air cant be as efficient as a properly designed low static pressure system. Here in Pa. my home is 3800sq ft. cooling it with a 3-ton system. On a 90 deg. day it doesnt shut off until 10 PM, humidity never over 47%. As I mentioned before, I am sure there are places that hv's would work well, I just havent come across one yet. Keep it cool Rian S.

Mark_46

Yes I have

I requested seperate quotes from my to-be installer. He was kind enough to write up three proposals; one for conventional forced hot air (heat and AC) which we did not choose but wanted the quote just for price comparison, one hydronic conventional (heat and AC) and one hydronic high velocity (heat and AC). The only difference between the two hydronic proposals (more or less) are the air handlers and duct type. The high velocity system was 11% higher.

David_5

Ductless

I don't see ductless as a great alternative. They are pretty expensive to buy. Many customers don't care for the looks. If you have to service them, part of the equipment is in the living space. Most have electronics in them and they can be difficult to trouble shoot. I don't recall seeing a ductless unit that had a higher seer than the minimum required. If the area to be cooled is broken up by walls then a ducted system is better.

David

Mark Hunt

Mitsubishi SEER ratings


I am looking at the Mitsubishi ratings. The lowest is 13.0 and the "Inverter" series goes as high as 17.0.

As for servicing, I have never had a Mitsubishi system break down.

Mark H

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David_5

I stand corrected

I didn't know about the higher seer models.
I have had to service Mitsubishi units and found them worse than others. The tech support was very poor. Thats just my experience.

David

johnny4

hi velocity is suitable when done well

Like many HVAC issues, the proper design & installation can make a lot of difference in the end performance. I was living with room a.c. in my 1939 brick hydronic-heat colonial in the Virginia suburbs of Washington DC for many years, until a better half moved in and let me know central a.c. would have to be part of the deal. We had a 2.5 ton system put in (the contractor's load calc was about 2.8 tons and he wanted to go to 3, I insisted on 2.5). The Unico/Spacepak works well with one central return. It isn't whisper quiet (neither were the window a.c.) but the overall comfort and performance is much superior to what we had had.

The high-velocity systems are indeed intended for use in older homes with less flexibility to accomodate ductwork. The closet space is already too small without having big ducts chewing up more volume for only 3 months of the year. Would I put a high-velocity system in a new home? No. But retrofit for existing is just the ticket.

ChrisL

Hi V efficiency

In the real world, the Hi V systems do get a bonus by dehumidifying better. If someone is setting the thermostat to comfort instead of some arbitrary number, they will probably set the temp a little higher, i.e less run time of the energy robbing blower.

Mike T., Swampeast MO

HV systems require significantly more engineering than standard systems. In that regard they're sort of like old gravity heating systems--maybe that's why I like them...

"Snowflakes" from the supplies are almost certainly due to unacceptably low air volume. At high velocity, friction in those little tubes increases greatly with length. "Forget" to compensate for longer runs and you'll have severe problems.

clammy

unico

I am now installing a unico in a brady bunch type home and if i was not using a hi vee system they would not be getting a/c installed .I use unico 's when there are no closets and it's a finished home on this job i used 18 unico side weall outlets and 14 standard unico registers and of course this job will be more costly then the conventinal system but the amount of space and getting the runs to some of the rooms would have been a nightmare and with some costly renovation to boot .Hi vee system are great when they want a/c and there little room and you don't want to get invouled in re sheetrocking 1/2 the home and you also want to have some closets left when all is done .In my opion cost wise it's about 1/3 more then a conventinal system just on the registers and air handler .I have used unico equipment and installed them for about 10 years and every homer i have done there was no remodeling and they have worked very well and very quite if done properly .PS istill do seperate supply returns for 2 nd floor beds .Peace and good luck clammy also heard mistibushi has a new 410a mr slim i was told it is 14 seer yea ha

Techman

SpasePak

Hi I put in a SpacePak hydroair system in a "design and engineered house" H.V.air was spec. The install was done in 1986, I had to be "Factory Certified" by attending a several hour class .Customer is happy ,which makes me happy.

John Mottinger

Single Central Return for High Velocity Air Conditioning

Mark, liked what you wrote.. But you missed a very important point.....

High Velocity systems run on only 1/2 as much cfm. ( 5 ton is 1150 CFM)...

The reason that one central return in a common area of the house works as well as it does is due to amount of air returned... (That's also why they can reduce the latent energy in a home by 30% more that conventional systems....)

John Mottinger

Single Central Return for High Velocity Air Conditioning

Mark, liked what you wrote.. But you missed a very important point.....

High Velocity systems run on only 1/2 as many cfm. (5 ton unit is 1150 CFM)...

The reason that one central return in a common area of the house works as well as it does is due to the lessor amount of air returned... (That's also why High Velocity can reduce the latent energy in a home by 30% more that conventional systems....)

A bedroom that's 12x12 on an corner of the house with a couple windows typically would use one outlet, that's 40 cfm... As long as there's 1/4" of a space under the door, the air being introduced into the room will pass under the door and back to the return.

Think of it this way... If you turned that bedroom upside down and filled it to the top with water, would it stay in the room???

Ahhh Grasshopper....

John Mottinger

Seer ratings and High Velocity Systems

Ted... you know of what you speak..

But, I couldn't resist this one.....

First the current minimum SEER requirement for all ARI -rated High Velocity systems is 11... not 13...

However, if any of you are as old as I am, you'll remember when the AGA~DOE have no ability to measure the effects of condensing exhaust gases and the credit that gives to Thermal and AFUE ratings. Back in the day, the maximum eff. was 88%...... Thank God they got that straightened out but, the same thing is going on now with ARI and high velocity..

Everyone agrees that High Velocity is profoundly more effective at removing humidity in the form of latent energy from the conditioned air in the home...

However, the ARI does not base it's test data on this latent ability... It looks mostly at sensible conditioning.

The drag about this is that High Velocity systems are fundamentally less in cost to operate that even a high SEER conventional.. But, there's no way to prove it. (unless you own one)

A pratical explaination of this is the differance between a day when when it's 75 degrees and 80% RH..

Now compare that to a day when it's 75 and 60% RH..

Same temperature but the later's much more comfortable....

The T'stat in a high velocity cooled house can be set at a higher temperature than conventional and the same, (in fact, better) comfort conditions can be had..

That means less condenser operation and savings..
Sorry if I sound like a commercial but there's so much mis-inforamtion about high velocity AC...

thanks..

JackFre

To Ductless...

Please look into this a bit further. First, the requisite disclaimer...I represent Fujitsu in New England. Having said that, the technology on the inverter based mini-split is just amazing. The Fujitsu 9K, 21 SEER inverter unit will modulate from 3,600-12,000 btu in cooling and being a heat pump will modulate from 3,000-18,000 btu in heat at 47F and 3-12,000 at 17f (HSPF 11/EERclg/htg 13.4/14.5). Now, in the northland a hp is not a sole source of heat...let me repeat that, in fact repeat along with me... but the consumer today needs to use all available options/resources to arrive at "annual economies". These units in Sept, Oct, Nov, late March, April, and May can be effective and the single stage boilers/furnaces can then be run when the weather is actually cold enough to allow them to run efficiently. Another key element to mini-splits, at least the Fujitsu's, is that the equipment has gotten smaller. The 18k evaporator is 18" smaller than last years at only 31". The 24 (18seer), 30 (18 seer) and 36 (15 seer)is 10" shorter at 39". The 36k condensing unit is 40% smaller than the old 10 seer. On our inverter units the minimum seer is 15 ranging up to 21 seer. This technology is going to do for cooling what the modulating gas valve has done for heating. True variable speed cooling! Neat stuff, IMHO!

As to why you would want a high seer unit...The Boston Globe had an editorial a couple weeks ago comparing the elec rates for UI, Nstar and municipal lighting districts. Nstar was up the most at almost 80% since 2004(?), I have the article at the office and can check later for exact dates/#'s), while munis were up 20%. In todays energy environment I cannot recommend making a buy decision based upon TODAYS cost. Do you think the energy picture is going to improve. I think most of the manufacturers pushing low seer are those who didn't make the investment, or couldn't, achieve the results.

I'd invite you to look at Fujitsugeneral.com. All the specs, submittals, install, operation and troubleshooting specs are there. If you go to the contractor log in, using "installer and 1ton12kbtu" for username and password respectively, there is a heat gain program for you also. Please check it out!

Ted_13

indeed a fish..

and one hell of a fight. Imagine trooling at 15 knots and a fish hitting your lure at 60 Mph. Bizzzzzzzzzzzzzz!!!!

http://www.nippersbar.com/

Ted_13

Good point

John, how SEER relates to actual energy efficiency of running the system in the real world is questionable. Before I installed my system I ran three window shakers (all 115 volt ? amps) as oposed to one unit 230V 1.8 amps + condenser 230V (? 15amps). I'll see if I can dig up some old electric bills to check it out. I do know that now I can make toast even when it's hot out. This also relates to a point made about mini splits. how many do you need to cool your whole house? Do you put one in every bed room?

Ted_13

less engineering than conventional

I think there is less engineering than a properly engineered conventional system because all the duct is the same. To properly engineer a conventional system using manual D for duct and register sizing takes some time. Granted there are some different rules with High Velocity compared to conventional but after installing a few of them you know what to look out for. With all duct and registers being the same if you continue to install the product you generally end up with a few leftovers that can be used on the next job.

Ted_13

Balancing High Velocity

That is true Jed. I'm curious, do you rely on the calculation or do you use an air flow meter on site?

Jed_2

Calculations

are done in pre-installation phase. It is difficult at best to be accurate with branch lengths based on floor plans. Site planning is very important. Then, the meter fine tunes it. I am not a contractor/installer, but have worked with contractors in this regard. But, I have not done many systems, just a few. I have learned a great deal from Chris Jacques, particularly on the Stephen King project. Chris is "top shelf" in my opinion.

Jed

Jed_2

Calculations

are done in pre-installation phase. It is difficult at best to be accurate with branch lengths based on floor plans. Site planning is very important. Then, the meter fine tunes it. I am not a contractor/installer, but have worked with contractors in this regard. But, I have not done many systems, just a few. I have learned a great deal from Chris Jacques, particularly on the Stephen King project. Chris is "top shelf" in my opinion.

Jed

p.s. How could I forget the tireless support effort, and system guidance, of Dino?