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Air Conditioner Ducts for a small studio?
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glenn Taylor
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11th April 2010
Old 11th April 2010
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Air Conditioner Ducts for a small studio?

Hello there I was wondering how do run the return ducts for a small 12x24 building with two rooms without sound leaking outside?
GT.
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11th April 2010
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Cheap and simple way is to use thermally (and acoustically) insulated ducts.




regards

Boggy
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11th April 2010
Old 11th April 2010
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Quote:
Originally Posted by moracspace View Post
Hard metal duct with lined interior.The flexible insulated ducting in some states is not acceptable due improper R values.Plus,the round duct causes stratification increasing the air noise at each diffuser.Trust me on this one,its my day job for 22 years.The ultimate solution would be ductless splits w/ 22db of air noise.
Although I will agree that these units are quiet - they will NOT solve your problem.

If you are code compliant - and I seriously suggest that you should be - you will require fresh air in your space. There are a couple of different ways you can accomplish this within the code - the first is to have operable windows that have openings that meet the code requirements for opening size. An alternate is a door that opens directly to the outside world. The 3rd is to have an adjacent room that meets one of those requirements large enough to provide air for both of those rooms- but then you cannot have a door between the 2 rooms - and the opening between them has to meet certain opening requirements that end up larger than a standard 3'-0" door opening.

The next method is mechanical ventilation - which must be dicuted directly to the outside world in each case.

But let's also talk reality here - even setting the code aside (assuming for a moment that you want to provide openings to the outside world that will make isolating your building acoustically even more difficult) - You are building basically an air tight box - and you need to provide fresh air in order to breathe unless you plan on working for very short periods of time and then opening everything to the outside world for a bit to replenish the air supply.

If you plan on working for any real length of time in these rooms you are going to need a fresh air supply that is always available...... and that means mechanically provided - a duct from the outside world into the space - and then (because these rooms really are almost completely air tight) a 2nd duct leading from the rooms back to the outside world in order to release the air pressure that will build up inside the space.

If you do not have the 2nd relief duct you will simply build up air pressure in the room until you reach the maximum static capacity of the fan - at which time no more air will move.

It's really that simple.

Typically I recommend that you construct a transfer box that is insulated inside with duct liner - which has multiple baffles inside of it creating a simple maze that the air has to travel through before entering the space -

The box is constructed with 3/4" plywood - as are the baffles - and then entire inside is lined with 1 1/2" 3pcf duct board - JM Superduct or equivalent (The board has a polymer liner so that the fiberglass fibers do not break free in therefore into your room and eventually your lungs over time)

Once the system is put together you add drywall mass to the outside opf the box to finish the isolation.

The final connection to the box needs to be a flexible connection to assure that you don't have a physical transfer from the duct into the structure. But that is typically 3' or less in my specs.

BTW- I agree with moracspace with using hard lined duct versus insulated flex - for another reason as well as insulation - and that is because you have better air flow (less restrictions) with hard duct than with you do with flex.

One other thing - if you go the route of a mini split system - you aren't going to be able to make use of the cooling coils of the air handler to treat the air coming into your space - which means that you have to do something on the fresh air supply to make up for this - in your case - cooling down the air you're pumping into the room - possible even adding some dehumidification in order to keep humidity levels in your space within reason (no need to create a perfect breeding ground for mold).

Dehumidifiers are easy to install and would tie into a humidistat installed in your room - but to temper the air you would require the addition of an HRV (Heat Recovery Ventilator - which also works to cool down outside air - but does NOT dehumidify) to temper the outside hot air - thus lowering your overall energy needs.

I do NOT recommend the use of of an ERV (which can dehumidify) because the dessicant wheels used in many ERVs become saturated fairly quickly and the moisture transfer mechanism becomes less effective with successive hot, humid periods

I hope this helps...........

Rod
glenn Taylor
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11th April 2010
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Thanks for the info gents! it is going to take me a while to figure out what to buy with that info in mind. Maybe that should have been my question. What's a good AC system for a 12x24 building with two rooms. There will be two windows on 1 of the long sides 3 feet from each end. Whats good? A window unit, split system, package unit, Mr Slim? I am in Florida. It's a swamp for 5 months a year starting in about 2 weeks.
GT.
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12th April 2010
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Quote:
Originally Posted by moracspace View Post
Obviously your not familiar with all ductless splits.There are now available and have been for several years ductless splits with a fresh air intake.BOCA new national code requires 20% fresh air into any space regardless if its sealed or contained.That being said look into the ductless splits or go with hard duct.If you are not following any codes and dont plan on an inspection,do what ever you want.BTW this doesnt mean you need air changes,just required to bring in 20% fresh air.This is off the topic anyway.
moracspace.

I am very aware of mini-splits that include fresh air - however I have not been able to find a single manufacturer who provides (or will provide on request) the AMOUNT of fresh air being provided.

Please provide me with the name of any manufacturer who provides that data on these units - I would really like to find out the answer to the question.....

Now - there is no new BOCA Code - the last BOCA Mechanical Code was the 1999 edition - Perhaps you refer to the International Mechanical Code which is the mechanical code used in Florida.........

The 2007 Florida Mechanical Code (which is the current code in FL)- Section 403.2 Outdoor Air Required (IMC as modified by FL)states:

Quote:
TABLE 403.3 REQUIRED OUTDOOR VENTILATION AIR

......................................ESTIMATED..................OUTDOOR AIR
..................................MAXIMUM OCCUPANT........[Cubic feet per
...................................LOAD, PERSONS PER...........minute (cfm)
..OCCUPANCY.....................1,000 SQUARE.................PER person]
..CLASSIFICATION.....................FEET(a)...................UNLESS NOTED

Stages, studios..........................70...............................15
As I said - this is straight from their current code - these items are not noted - you can always research this for yourself if you wish.

You might install these systems as a your year round job - but i design recording and movie studios all over the world - along with HVAC Systems (although I will admit I have not headed up the design of anything over $10,000,00 in scope) - and if anyone is building anything that even begins to resemble an acoustically isolated building or set of rooms - whether or not they pulled permit they would be brain dead to ignore fresh air for their rooms.

I am amazed that anyone in the trade would suggest such a thing - apparently you have never worked on HVAC for air tight rooms.......

To the OP - if you have operable windows - these are the requirements of the Florida Mechanical Code for natural ventilation so you might understand the proper sizing of those windows:

Quote:
[B] SECTION 402
NATURAL VENTILATION

402.1 Natural ventilation. Natural ventilation of an occupied
space shall be through windows, doors, louvers or other open-
ings to the outdoors. The operating mechanism for such open-
ings shall be provided with ready access so that the openings
are readily controllable by the building occupants.

402.2 Ventilation area required. The minimum openable
area to the outdoors shall be 4 percent of the floor area being
ventilated.

402.3 Adjoining spaces. Where rooms and spaces without
openings to the outdoors are ventilated through an adjoining
room, the opening to the adjoining rooms shall be unobstructed
and shall have an area not less than 8 percent of the floor area of
the interior room or space, but not less than 25 square feet (2.3
m^). The minimum openable area to the outdoors shall be based
on the total floor area being ventilated.
BTW - this requirement means you cannot block these off with the typical window seals a lot of people make for sound when they want to keep their windows but also want isolation from the outside world.:

Quote:
The operating mechanism for such openings shall be provided with ready access so that the openings
are readily controllable by the building occupants.
I have to admit though - i find myself a bit confused as to what isolation you are concerned with - if it is not the outside world - what exactly is it?

Rod
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12th April 2010
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Quote:
Originally Posted by glenn Taylor View Post
Thanks for the info gents! it is going to take me a while to figure out what to buy with that info in mind. Maybe that should have been my question. What's a good AC system for a 12x24 building with two rooms. There will be two windows on 1 of the long sides 3 feet from each end. Whats good? A window unit, split system, package unit, Mr Slim? I am in Florida. It's a swamp for 5 months a year starting in about 2 weeks.
GT.
It depends - what are the uses of the spaces involved?

If one is a control room and the other a tracking room - then the HVAC needs are very different -

HVAC is based on a few different design requirements - he first being Sensible Loads the other being Latent Loads.

Sensible loads are loads based on mechanical and electrical items that introduce heat into the space but do NOT introduce humidity.

Examples of this would be your lighting - computers and recording gear, thus your board - your compressors, amps - powered speakers, etc.

Typically you will have a ton more gear in the control room putting out heat than you will in the tracking room.

Latent loads are loads that introduce both heat AND humidity - so people, fresh air, in homes that would include kitchens (cooking, washing dishes, etc) bathrooms - etc., etc.

IN a control room people are generally relaxed and seated - whereas in the tracking room they are usually working their butts off - and putting out a lot of heat and humidity.

This is one of the reasons that it is difficult to provide a single HVAC system to handle both rooms......

The amount of heat that people put out varies tremendously depending on what they are doing, for example:

To accurately calculate the Btu output of a person, you first have to
determine their BSA (Body Surface Area). To determine this, you could
use one of several mathematical models available. I prefer the Mosteller
formula, but other popular methods exist. My reason for preferring
this formula over the others only has to do with the ease of use this one
presents. The calculations can be performed with a simple handheld
calculator.

The Mosteller formula is:

BSA (m2) = ([Height(cm) x Weight(kg)]/3600)* .5

A person 5'-10" tall (177.8cm) weighing 180.78 pounds (82kg) would
have a BSA of 2.02594m2

BSA (m2) = ([177.8cm × 180.78kg ]/3600)* .5 = 2.02594m2

To convert meters2 to feet2, simply multiply it times 10.7639104. So this person would have a BSA of 21.807 feet, and let’s call him Mr. “A.”

Mr. “A” will produce (in a typical office setting) 482.81Btu/h (22.14Btu/h × 21.807 feet2) (141.48watts/h ).

A person who is working hard has a Met Rate of about 3.0 - and I know when I am jamming my ass off it is as physical as anything i do - so using this Met Rate Mr "A" is going to produce 353.56w/hr or about 1207 Btu/h.

That's roughly 2 1/2 times as much heat output. But not just heat - it is Latent - containing humidity.

When you design using standard commercial split system it's easy - you simply choose the system you want based on the latent / sensible loads that meet your needs and are listed as a part of the manufacturer's design.

But - this info does not exist for mini-split, through the wall or window type air conditioners - they are a generic sort of one size fits all - which is why people end up needing to add either humidification or dehumidification or sometimes both depending on whether or not fresh air is an issue.

So (in my mind) everything begins with what your real needs are.......... is this going to be a serious project studio - or just a place where you jam and occasionally make a 1/2 way decent demo tape?

Rod
glenn Taylor
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13th April 2010
Old 13th April 2010
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Usually 1 to 3 people in the two rooms . i want to overkill a bit So if the total area is 12x24x8=2304 square feet round up to 2500 square feet. BTU=?
GT
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13th April 2010
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Quote:
Originally Posted by glenn Taylor View Post
Usually 1 to 3 people in the two rooms . i want to overkill a bit So if the total area is 12x24x8=2304 square feet round up to 2500 square feet. BTU=?
GT
Not cubic feet - square feet - 12 x 24 = 288 s.f. = 3 people = 45 cfm minimum

or

the windows (when fully open) need to have a minimum of 11.52 s.f. of free open space between the 2 - so 5.76 s.f. apiece. Interestingly - the minmum size required for an egress window in a bedroom is 5.7 s.f.

So open your windows fully and measure the free opening to figure out if they meet the code requirements.

I am still waiting to hear what exactly you are trying to isolate your rooms from?

BTW - when it comes to Air Conditioning - oversizing is a bad idea - even though a lot of HVAC contractor's do it all the time.

They say to home owner's that a ton and a 1/2 of cooling is what you need - but we will install a 2 ton unit and then in the worse heat during the summer you will always have plenty of cooling.........

WRONG

If you need a ton and 1/2 you should have a ton and 1/2 - when units are oversized not only do they not dehumidify properly (due to the fact that they have short run cycles) but the compressor runs more often - and (from an energy cost point of view) the longer run times you have for the compressor the cheaper they are to run - the most energy consumption is during the compressor start-up.

I also want to add that the BTU consideration from people is only one piece of the puzzle - to accurately determine your needs you have to take into account each and every piece of gear you will have in each space - the lighting load (what heat the lighting adds to the load) as well as the fresh air, passive solar gain through your windows (if they are subject to the sun) and heat gain/ cooling loss through the building's envelope. Although - as regards the last - if you are building a super isolated room (room within a room construction) you will wind up with little or no solar gain / cooling loss - when you start talking air tight construction with roughly R40 wall assemblies and R 50 roof assemblies, there is so little loss taking place that from a design point of view you can walk away from that part of the equation.

I have a small spreadsheet that I can email you for doing the calculations - although it does not include the added latent load with the fresh air - you will have to determine that for your area and add it in........

let me know what you would like

Rod
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13th April 2010
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Yea a spreadsheet would be nice. I was thinking of using the main wall. Put 2 layers of 5/8" drywall between the studs. Put 1 or 2 2'x4'x1" sheets of insulation then 2 more layers of 5/8" drywall nailed to the studs. Building in back yard. Shopping center behind. No sound prob Left house way over. House to right is close. 80 ft. Should be ok. What is a good ac system. A mini split system?
Glenn
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Quote:
Originally Posted by glenn Taylor View Post
Yea a spreadsheet would be nice. I was thinking of using the main wall. Put 2 layers of 5/8" drywall between the studs. Put 1 or 2 2'x4'x1" sheets of insulation then 2 more layers of 5/8" drywall nailed to the studs. Building in back yard. Shopping center behind. No sound prob Left house way over. House to right is close. 80 ft. Should be ok. What is a good ac system. A mini split system?
Glenn
Glenn, can you draw me a sketch? I still do not have a clear picture of your needs - if you do - indicate the landmarks you are referring to - with approximate distances......

Hey - I am in the middle of a design right now - and am taking the mini split direction - BUT - I am also including a separate fresh air system.

That (right now in Rhode Island) is about the least expensive way to go (with the exception of either through the wall or window- but with them you have isolation isues).
glenn Taylor
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14th April 2010
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Ok thanks again Rod for your help. Here is a idea I have for a layout.
The shed will not arrive until around Monday Next week. I was trying to figure out what AC system would be good. For now I will keep the dbs inside to 90 or less. One vent in each room. A return somewhere. I still have a week or so before adding drywall,insulation to walls. if I forgot something let me know?
GT.
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