Hello:
I'm newly registered here and this is my first post. Please be lenient if I break any of the rules--I'm trying.
I'm a student in an acoustics program here in the US. I'm wondering about the best approach to HVAC for recording studios (commercial rather than home-based). I understand many basic construction methods, but I don't know thing one about HVAC. All I've really learned thus far on the topic is very general: oversize the system to reduce air velocity, and keep dampers away from the most sound-critical areas. I'd like to hear anything anyone's got to share on this topic, and the more specific, the better. This evening I've been reading about chilled beam systems, both active and passive. One of the supposed advantages is reduced noise, and I understand basically why, but I don't understand how such a system would interface with, say, the building-wide HVAC system in an office building (again, assuming a commercial recording studio in an urban setting). Can anyone address this or just share their advice on how best to design/spec HVAC in such a situation?
Thanks,
EZ
Acoustics Student
HVAC general
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Acoustics Student
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Soundman2020
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Re: HVAC general
Hi there EZ, and Welcome! 
HVAC in studios is a huge subject, so you certainly have your work cut out for you! When I'm designing a studio, I often spend as much time on the HVAC system as I do on the structural and acoustic aspects...
The basic concept is:
- Calculate the volume of the room, and assume you need to circulate that volume 6 times per hour (minimum, preferably 8 )
- Of that circulating volume, you need to exhaust somewhere between 20% and 35% to the outside world, and replace it with the same volume of fresh air.
- If the room is high occupancy (eg, small live room for tracking an orchestra or choir), you might need to increase both of those, to ensure that you are removing enough CO2, and replacing it with enough O2 to keep everyone happy, healthy, and (worst case) alive.
- Once you know the total volume of air that you will be moving (air flow rate), you need to figure out how big the registers need to be, to keep the air flow velocity below 300 fpm.
- With all of that in mind, you can calculate the sizes of your ducts and silencer boxes (sometimes also called "baffle boxes" or even "mufflers").
- The silencers need to be designed with a certain insertion loss in mind, which means "how much sound do the stop?" The insertion loss of each silencer needs to be similar to the design isolation level of the room it is attached too.
- You can increase insertion loss by making the box heavier (more mass in the building materials used to make it), longer, putting more baffles in it, thicker baffles, having several changes in air flow direction, and changing the cross-sectional area by a factor of at least two (preferably much more).
- All of that increases the static pressure of your air flow path, so you need to take care to keep it within the range of the fans and/or AHU that y9u intend to use to drive the air through it.
- If your static pressure is too high, the fan won't be able to move the air correctly, the fan blades will stall / create turbulence / be noisy, the motor will work too hard and burn out too soon. Etc.
- To dimension the actual cooling capacity of the AHU, figure out the total heat that will be produced in the room from things like people, lights, equipment, hot food, musical instruments, etc, plus take into account the climate (hot air coming in through the fresh air duct from outside), plus possible heat coming in through windows, walls, roof, etc (usually not an issue in studios). Calculate all that in watts, convert to BTU or tons of cooling required.
- That's your sensible heat load, but you also need to consider the latent heat load: due to humidity in the air. The AHU cannot actually cool the air much if it is very humid, until the humidity is first removed... which happens by condensation on the cooling coils inside the AHU. So you need to factor in the latent heat load in the studio, from the climate itself and from the moist air exhaled by the people, and from any other sources (if there's half a dozen pizzas in the room, and twenty beer mugs, that's extra moisture... ). Convert the latent heat load to BUT or tons, as above.
- The capacity of the AHU needs to be sufficient to handle both the latent heat load and the sensible heat load for the worst case scenario: Room fully occupied by a bunch of hot, sweat, smelly musicians on the hottest most humid day in mid summer, with all of them eating and drinking copiously, while the jam hard and fast, getting hotter and sweatier, producing a lot of body heat, and exhaling lots of moisture, with all the lights, equipment and instruments going full bore.
- It also needs to be able to deal with the other "worst case scenario": one single person in the room, sitting quietly, doing nothing at all, with most of the gear and lights off, and no food or drink.
- The AHU needs to be able to handle both of those while maintaining RH at around 40% or so, and air temperature in the room at around 21° or so.
- If you have multiple rooms, then do the above for each of the rooms separately. Assuming you have once single AHU for all of them, then you'll also need to design a control system that automatically adjusts the flow to each room as needed, sensing changes in the conditions inside the room (temperature, humidity, CO2 level, etc)
- In all cases, try to keep the AHU outside the acoustically isolated area of the studio. Even the very quiet AHU's are still too loud for most studios. We normally design home studios for NC-20 or so, and professional studios for NC-15 or less.
That's the basic procedure. In reality, it's more complicated....
That's about it!
Simple!
Look around the forum at some of the larger studio build projects, and you'll find more detailed information on how to do this.
- Stuart -
HVAC in studios is a huge subject, so you certainly have your work cut out for you! When I'm designing a studio, I often spend as much time on the HVAC system as I do on the structural and acoustic aspects...
The basic concept is:
- Calculate the volume of the room, and assume you need to circulate that volume 6 times per hour (minimum, preferably 8 )
- Of that circulating volume, you need to exhaust somewhere between 20% and 35% to the outside world, and replace it with the same volume of fresh air.
- If the room is high occupancy (eg, small live room for tracking an orchestra or choir), you might need to increase both of those, to ensure that you are removing enough CO2, and replacing it with enough O2 to keep everyone happy, healthy, and (worst case) alive.
- Once you know the total volume of air that you will be moving (air flow rate), you need to figure out how big the registers need to be, to keep the air flow velocity below 300 fpm.
- With all of that in mind, you can calculate the sizes of your ducts and silencer boxes (sometimes also called "baffle boxes" or even "mufflers").
- The silencers need to be designed with a certain insertion loss in mind, which means "how much sound do the stop?" The insertion loss of each silencer needs to be similar to the design isolation level of the room it is attached too.
- You can increase insertion loss by making the box heavier (more mass in the building materials used to make it), longer, putting more baffles in it, thicker baffles, having several changes in air flow direction, and changing the cross-sectional area by a factor of at least two (preferably much more).
- All of that increases the static pressure of your air flow path, so you need to take care to keep it within the range of the fans and/or AHU that y9u intend to use to drive the air through it.
- If your static pressure is too high, the fan won't be able to move the air correctly, the fan blades will stall / create turbulence / be noisy, the motor will work too hard and burn out too soon. Etc.
- To dimension the actual cooling capacity of the AHU, figure out the total heat that will be produced in the room from things like people, lights, equipment, hot food, musical instruments, etc, plus take into account the climate (hot air coming in through the fresh air duct from outside), plus possible heat coming in through windows, walls, roof, etc (usually not an issue in studios). Calculate all that in watts, convert to BTU or tons of cooling required.
- That's your sensible heat load, but you also need to consider the latent heat load: due to humidity in the air. The AHU cannot actually cool the air much if it is very humid, until the humidity is first removed... which happens by condensation on the cooling coils inside the AHU. So you need to factor in the latent heat load in the studio, from the climate itself and from the moist air exhaled by the people, and from any other sources (if there's half a dozen pizzas in the room, and twenty beer mugs, that's extra moisture... ). Convert the latent heat load to BUT or tons, as above.
- The capacity of the AHU needs to be sufficient to handle both the latent heat load and the sensible heat load for the worst case scenario: Room fully occupied by a bunch of hot, sweat, smelly musicians on the hottest most humid day in mid summer, with all of them eating and drinking copiously, while the jam hard and fast, getting hotter and sweatier, producing a lot of body heat, and exhaling lots of moisture, with all the lights, equipment and instruments going full bore.
- It also needs to be able to deal with the other "worst case scenario": one single person in the room, sitting quietly, doing nothing at all, with most of the gear and lights off, and no food or drink.
- The AHU needs to be able to handle both of those while maintaining RH at around 40% or so, and air temperature in the room at around 21° or so.
- If you have multiple rooms, then do the above for each of the rooms separately. Assuming you have once single AHU for all of them, then you'll also need to design a control system that automatically adjusts the flow to each room as needed, sensing changes in the conditions inside the room (temperature, humidity, CO2 level, etc)
- In all cases, try to keep the AHU outside the acoustically isolated area of the studio. Even the very quiet AHU's are still too loud for most studios. We normally design home studios for NC-20 or so, and professional studios for NC-15 or less.
That's the basic procedure. In reality, it's more complicated....
That's about it!
Simple!
Look around the forum at some of the larger studio build projects, and you'll find more detailed information on how to do this.
- Stuart -