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HVAC for project studio/practice space. Please help!!
Old 3rd April 2019
  #1
Here for the gear
 

HVAC for project studio/practice space. Please help!!

Hello,

I'm in the process of building a project studio/practice space in an external garage/shed in my back yard. I'm at a point where I really need to determine and commit to a solution for AC/heat and ventilation before proceeding much further on the build. The more I research, the more confused I seem to get. I'm hoping someone with some experience/knowledge can help me out.

The space is going to consist of a 336 sq. ft. live/practice room and a 180 sq.ft control room (as well as small amp iso room and storage closet). After initial research, when first discussing possible plans a few years ago, I suggested I would get an ERV to supply fresh air (with baffle boxes to the rooms) to my live and control rooms. I would use baseboard heat and eventually a mini split for AC (at the time I was unaware of mini splits containing heat pumps). This plan was criticized by one of the forum users, saying I wasn't addressing humidity at all and my electric heating bills would be terrible. He strongly suggested a fully ducted HVAC solution, saying that would take care of humidity, and would be much more efficient.

I'm assuming that means something like this??
Pioneer(R) 18,000 BTU 19 SEER Ceiling Concealed Ducted Mini-Split Air Co – Pioneer Official Store

Which if so, would be fine. Except for I don't understand how fresh air is integrated into a system like this.

Also, the more research I've done on the forum, the more posts where I've seen Rod Gervais chime in, it seems to me that his suggestions for his builds are basically what my original idea had been (except just starting with wall mounted mini splits with heat pumps). So an ERV for fresh air, and then something like this (with 1 unit in the live room, and 1 in the control room):
Mitsubishi M2H20W09090000-A 18,000 BTU 20 SEER Ductless Dual Zone Heat Pump System 9+9

Is there something I'm not understanding?

I live in North Dakota, where humidity is normally not too much of a problem. However, while not necessarily the norm, 110F on the hottest summer days, and -20F (or worse) on the coldest winter nights, are not unusual. The build will be very insulated, room-in-room designs, with both the inner and outer leaves VERY well sealed. It will definitely be completely air tight.

I'm hoping someone can point me in the right direction.

Any info would be greatly appreciated!
Old 3rd April 2019
  #2
Here for the gear
 

I should note a few other things for extra info. Although I bought Rod's book and have read through the HVAC section a number of times, I'm still struggling to put it all together. I did add start on a few of the calculations included in the book, which I'll include:

Live/practice room:
1 - 30 Watt guitar amp - 30 watts x 3.4129 = 102.387 Btu
1 - 100 Watt guitar amp - 100 watts x 3.4129 = 341.29 Btu
1 - 300 Watt Bass amp - 300 watts x 3.4129 = 1023.87 Btu
1 - Studiolive Mixer - 100 watts x 3.4129 = 341.29 Btu
1 - QSC RMS 2450 power amp - 1500 watts x 3.4129 = 5119.35 Btu
1 - Mini Fridge - 60 watts x 3.4129 = 204.774 Btu
4 - Adult Humans (active) - 1414.24 watts x 3.4129 = 4826.66 Btu
Lighting - Area (sq) of room x 2 - 336 x 2 = 672 Btu

Total maximum live/practice room - 12,631.62 Btu/hr.

12,631.62/12,000 = 1.053 tons of cooling per hour

Control room:

Monitors/Sub - 480 watts x 3.4129 = 1638.192 Btu
Computer/Screen (est) - 225 watts x 3.4129 = 767.903 Btu
Monitor controller and interface - 50 watts x 3.4129 = 170.645 Btu
1 - Mixer - 40 watts x 3.4129 = 136.516 Btu
1 - 100 Watt amp - 100 watts x 3.4129 = 341.29 Btu
4 - Adult Humans (inactive) - 643.76 x 3.4129 = 2197.089 Btu
Lighting - Area (sq) of room x 2 - 180 x 2 = 360 Btu
Misc other gear - 250 watts x 3.4129 = 853.225 Btu

Total maximum control room - 6,464.86 Btu/hr.

6,464.86/12,0000 = 0.53 tons of cooling per hour

FRESH AIR -

15 cfm/person

Live Room & Control Room - 60 cfm

I should also note that although I want to do things as properly as reasonably possible, this is NOT a commercial studio or even really a space for a "part-time gig". The VAST majority of time will be me writing/practicing/mixing alone or with a few friends, and on occasion just local acquaintance bands. The above calculations represent a "worst case scenario" of both rooms, but it will basically never be the case that BOTH the rooms will be generating that heat at the same time.

Thanks in advance for any help!

Sean
Old 3rd April 2019
  #3
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Starlight's Avatar
 

Sean, I am no expert but I have gone through the same process that you are going through, albeit without separate live and control rooms.

Of the two AC units you linked to, the Pioneer system can only operate as quiet as 36dB which is too loud for studio use. The Mitubishi unit operates as quiet as 19db which is quiet enough (on the lowest two settings) and is among the quietest AC units you can buy.

From my reading, in smaller rooms like you and I have, separate mini-split AC and a ventilator usually are more efficient than a combined fully ducted HVAC unit. That is the opposite of the forummer that criticised your design, so definitely read further on that until you are confident which will be best for you. I did most of my learning from books by Rod Gervais and Simon Newell plus this forum. One more thing on the ventilator, bsed on my studying I chose an HRV instead of an ERV. Your climate seems similar enough to mine that I would suggest you also study more about the right type for your use before buying. See posts 8 and 9 particularly in my studio build, here. I am pretty sure that lots of reading of this forum, and especially advice given by Rod helped me arrive at my choice - and sorry, I didn't bookmark all of his posts so I cannot give you a handful of links to speed up your research.

Again in post 9 in my build you will find my research into airflow.

I will do my best to keep up with you and at least help where I can. Fee free to ask.
Old 3rd April 2019
  #4
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Starlight's Avatar
 

Here is some reading for you: my final post in the topic Mini-Splits and BTUs, and Rod Gervais - but read the whole topic to get his comments in context - in the topics Ventilation and Mini Split AC -- pros and cons of self-install?
Old 3rd April 2019
  #5
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Perhaps the issue here is clarifying the "humidity" part. ANY air conditioner will control the humidity. An HRV will do nothing at all about humidity (it only exchanges heat between the incoming and outgoing air). An ERV can help somewhat with humidity control, provided that you live in a climate where there is a large difference in humidity between indoors and outdoors, but even then it will NOT fully control the humidity in the room.

It works like this: ERV's transfer not just heat but also humidity between the incoming and outgoing airstream. Whichever has the higher humidity will lose some of it to the other airstream. So, if your incoming air is very humid, then some of that will be transferred to the outgoing airstream, and thus will never get into your room... but some will. ERVs are not 100% efficient at transferring either heat or humidity, so even though most of the incoming humidity will go back out again, some will still get into the room. The amount of "some" depends on the design of the ERV, and the magnitude of the difference between the humidity in each air stream. Eg, if you have 95% RH in the incoming air, and 35% in the outgoing air, you'lld get good transfer, but if you have 45% in the incoming air and 40% in the outgoing, there will be practically no transfer. The same is true if you live in a very dry climate: the outgoing humidity can be transferred back to the incoming air-stream, but it won't be as efficient as going the other way, because the difference in levels can never be as large.

Thus, if you live in a climate where there isn't a large difference between indoor and outdoor humidity, an ERV would not be the right choice: it will still transfer heat, like an HRV, but the extra mechanism and expense won't be worthwhile. For that climate, just get an HRV.

However, HRV's have a similar situation, but with temperature, not humidity. They are also most effective where there is a large difference in air temperature between indoors and outdoors, and less effective if the difference is small. So if you live where it is -30°C outside and +20°C inside, yes, it is worth it. Ditto if it is +45°C outside and +20°C inside. Not so much if it is only 23°C outside and 20°C inside... So, once again, climate will dictate if an HRV is going to be worthwhile for you.

Summary so far: HRV's don't to anything to change humidity. ERV's do something, by transferring humidity between the air-streams, but that isn't the same as controlling humidity in the room: it's just exchanging some of what is already there. If your room has high humidity inside, all that an ERV will do is make sure that the humidity does NOT get sent outside! It will stay there. And if the high humidity is outside, an ERV will only remove some of that, not all, so the rest will get into your room.

An air conditioner, on the other, does actively remove humidity from the air. For a very simple reason: air conditioners get cold, and the humidity in the air condenses on cold surfaces. It's that simple. It does not matter if you have a ducted mini-split, or an ductless ((a.k.a. "unducted", "non-ducted")) mini-split or anything else: The simple fact of passing warm moist room air over the icy cold cooling cools inside the unit, causes the humidity to condense out as liquid water, which then needs to be drained away.

Now here's the problem with selecting the CAPACITY of your air conditioner: When that water condenses on the cooling coils, that heats them up! You probably already know that "evaporation is a cooling process": thus, when you sweat your body cools down because the sweat evaporates, taking heat with it. But the reverse is also true: "condensation is a warming process". As the water vapor in the air condenses into liquid water, it releases its "latent heat", and that warms up the cooling coils. Obviously, if the cooling coils got warm, then they can't cool the air! Their "cooling ability" was already spent on converting the humidity into water. So the air moving through the unit does not get cooler: it just gets drier.

Therefore, when you calculate what cooling capacity your HAVC unit needs, you MUST take into account both the sensible heat load (the hot things in the room, such as equipment, lights, coffee, pizza, and PEOPLE!), plus you must ALSO take into account the latent heat load of the air in the room. If you just figure enough cooling capacity for your gear, you will be way short.

For example, let's say you figured that you need 18,000 btu/hr to remove the amount of heat your gear puts out, but the humidity in your room is high, and it takes 6,000 btu/hr just to remove the humidity... then your air conditioner is only left with 12,000 btu/hr to do the actual cooling... Clearly, that's not going to work. The room will not get cool, and the humidity will probably also stay too high.

You need to take into account the latent heat.

OK, so let's say you did that as well, and figured that all your gear is 18,000 btu/hr, and 6,000 btu/hr for the latent heat, so you figure 24,000 btu/hr is what you need.... What about the people? People put out heat too (and also humidity....). The amount of heat that a person puts out depends on several factors, including body surface area, body weight, metabolism rate, activity, etc. The heat output can be anywhere between about 100 watts (small person at rest) and maybe 800 watts or even more (Olympic athlete in full exertion). Three people at rest is about 1,000 btu/hr, roughly. Six musicians jamming hard could be 3 or 4 times as much. So it's rather important to consider room occupancy and activity level, when figuring your heat load.

Plus, there's the issue of how much heat is still coming in with the fresh air that you are bringing in from outdoors. Even a good HRV won't transfer all of that to the outgoing air: some will make it through. And if you don't have an HRV; then ALL of that will make it through. So you need to factor that in as well.

In other words, there's a lot to take into account when figuring the capacity that you need! And you also need to allow some margin: If you figure that your typical heat load (including all of the above) will be 24,000 btu/hr, then buying a unit rated at 24,000 btu/hr would be a mistake, because it will always be running at full capacity.... and what happens when there's a heat wave going on outside, and each musician brought their WAGs along for the session? Overload! Leave a bit of margin. But don't go crazy with that margin either! If you figure 24,000 btu/hr, don't get a unit rated at 100,000 btu/hr! It will "short cycle", giving you sudden intense blasts of hurricane strength arctic freeze for two minutes, then stay off for an hour while the icicles melt and things get back to normal... then repeat. Allow a reasonable margin, but not crazy.

On the other side of the coin, you also want to make sure that when the studio is occupied by just one person sitting quietly in mid winter, with most of the gear and lights turned off, that the unit can run low enough to not freeze the poor guy!

It's all about balance.

But getting back to the original point: It does not matter if you have a ductless unit, or a ducted unit: they both do the exact same job. The only difference is where you mount it! The ductless unit obviously has to go in the room where it is needed, so if you have two rooms, then you need two units, one for each room, each sized correctly for that room alone. That implies noise in the room: even the quietest units do still make a noise, especially when they are running at full capacity. There's also sometimes the noise of the condensate water draining away... But if you have a ducted unit, then that can be mounted completely outside the studio entirely, so no noise at all gets in... and you can also just have one single unit to handle all the rooms, instead of a separate unit for each room.

In either case, ducted or not, you still need to supply fresh air to the room, and remove the stale air. That air might go through the HRV or ERV, if you have one, or if not then it just comes in direct from the outside, and dumps direct to the outside. The AMOUNT of stale air you remove must be enough to ensure that you remove all the CO2 (and other noxious gasses) being generated by the people in the room, and you then replace that exhaust air with fresh air from outside. So you therefore need enough air flow to ensure that the air circulates properly, with the fresh air fully mixing with the room air, moving through the entire room, then being sucked out through the exhaust register. That implies designing the system so the air flows evenly throughout the room. And that implies that you need a supply duct and an exhaust duct in EACH room, with there respective silencer boxes. This is true regardless of whether you use a ducted HVAC, or an ductless HAVC unit: You steel need the ducts, silencers, registers to supply/remove the air.

If you have a ducted system, then it's only slightly different. The difference is that you recirculate of the conditioned air through the rooms, through the same type of ducts as if you had ductless units, except larger. And you then extract the stale air from that recirculating air at some point on it's circuit, while adding the fresh air into the circuit at a point downstream from the exhaust.

So there's not actually a lot of difference! In both cases you need ducts. There's no way around that. With a ducted system, the ducts are just a bit larger, because the circulation rate is higher than for a pure "air replacement" system, but the same principle still applies: you have a supply duct for each room, and a return duct for each room, with their respective silencers, registers, etc. So that part does not change, except that the ducts are bigger. The only ADDITIONAL part in a ducted system, is that most of the return air is ducted back to the input side HVAC unit itself, to be cooled / dehumidified, then sent on its way around the same path again. Some of the return air is dumped overboard, just like in the ductless scenario, and the same amount of fresh air is added in, just like the ductless scenario. And also "just like the ductless scenario", you can have an HRV or ERV in that exhaust air / fresh air path if you want, to recover some of the heat that would have been lost otherwise.

So, overall, there just isn't a lot of difference in the concepts: In both cases you have ducts, and silencers, and registers, and fresh air intake, and stale air exhaust, and possibly an HRV or ERV, and an air conditioner. That doesn't change. It's only the minor details of where the ducts go and how big they are that change.

For a two-room studio, probably the biggest deciding factor is going to be cost: Two small ductless systems will probably cost you more than one single larger ducted system (especially when you consider the installation costs for two systems, rather than just one). And if you have three rooms that need HVAC, the decision is simpler still...

Personally, I prefer ducted. You can mount the actual AHU (Air Handler Unit) anywhere you feel like OUTSIDE of the studio, where it is easy to install, easy to service, easy to fix, easy to replace... and where it doesn't matter if it is noisy or not, because none of that will get into the studio. Pretty much all of the studios I design are done with ducted HVAC systems, and a single AHU. It's usually the simplest, and certainly the least expensive for a multi-room studio.

Hope that helps to shed some light on what is a rather complex subject.

- Stuart -

Last edited by Soundman2020; 3rd April 2019 at 09:09 PM..
Old 18th April 2019
  #6
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Wow! Thank you both for the quick responses and valuable information!! I'm sorry I wasn't able to respond sooner, but I spent a few days digesting the information you provided, doing some additional research based on this new knowledge, and spent some time recalculating on my numbers with this new information.

Starlight, I read your thread from beginning to end a few times. It was crushing to find your build thread ending in you losing your space. After seeing how few responses you received when looking for help, the fact that you are on here helping out others so willingly REALLY speaks volumes!

Stuart, your in-depth post helped me tremendously in understanding the full picture, and the possible options for tackling this issue. In particular, the latent vs sensible load issue - I had read through the section of Rod's book a few times, but it didn't click for me until I read your post. It really helped me in recomputing my numbers, taking humidity into account (which I'll include in a second reply after this).

Given the benefits Stuart listed for the ducted option, I'm inclined to think this might be my best bet. I do have one question that might be REALLY dumb, but here it goes....

- When you list the benefit of being able to place the AHU anywhere outside of the studio....do you mean ANYWHERE outside the studio....as in, is it possible for me to have the AHU and ducts for this thing in the unfinished/vented attic??? Is that a thing people might do? Even in my climate??

I've been keeping up with this gentleman's youtube with great interest, as we are in the process of similar builds. When I saw his HVAC setup all put together (at about 22:30 into this video: YouTube), I just have a feeling it can't possibly be that "easy" for me.

Even if so, and he mentions not having his ventilator set up yet, I still don't quite understand physically where and how fresh air intake/outtake is integrated/hooked up into these systems. If anyone could give me any information in regards to that, I would really appreciate it!!

Thanks,

Sean
Old 18th April 2019
  #7
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Here are my updated calculations (as best as I understand) taking latent vs sensible loads into account. I'm still not 100% certain, as even in Rod's book when he talks about the ventilation index information (1.0 latent vs 0.4 sensible for my area FYI), he states that it's "not just a factor you plug into your design calculation". This leads me to believe I may be making too big of an assumption (or just might be wrong) when dividing the Btus per year by the number of hours per year and adding that to my total?

Based on Stuart's post, and as I had previously stated that my live room calculation represents a "worst case" situation (the most people I expect in there, at full human activity factor, with ALL gear on at same time, I will probably go with LED lighting, etc), I would think an 18,000 BTU system should have me covered, with giving that extra margin to never have to be running at full capacity. My control room calculation, or possibly somewhere between the two, will be where things are at the VAST majority of the time. Does that seem reasonable??



Live/practice room (Gear and people calculation):

1 - 30 Watt guitar amp - 30 watts x 3.4129 = 102.387 Btu
1 - 100 Watt guitar amp - 100 watts x 3.4129 = 341.29 Btu
1 - 300 Watt Bass amp - 300 watts x 3.4129 = 1023.87 Btu
1 - Studiolive Mixer - 100 watts x 3.4129 = 341.29 Btu
1 - QSC RMS 2450 power amp - 1500 watts x 3.4129 = 5119.35 Btu
1 - Mini Fridge - 60 watts x 3.4129 = 204.774 Btu
Lighting - Area (sq) of room x 2 - 336 x 2 = 672 Btu
4 - Adult Humans (active) - 1414.24 watts x 3.4129 = 4826.66 Btu : (850 Btu/hr x 4 people = 3,400 latent load, 357 Btu/hr x 4 = 1,428 sensible)


Control room (Gear and people calculation):

Monitors/Sub - 480 watts x 3.4129 = 1638.192 Btu
Computer/Screen (est) - 225 watts x 3.4129 = 767.903 Btu
Monitor controller and interface - 50 watts x 3.4129 = 170.645 Btu
1 - Soundcraft mixer - 40 watts x 3.4129 = 136.516 Btu
1 - 100 Watt amp - 100 watts x 3.4129 = 341.29 Btu
Lighting - Area (sq) of room x 2 - 180 x 2 = 360 Btu
Misc other gear - 250 watts x 3.4129 = 853.225 Btu
4 - Adult Humans (inactive) - 643.76 x 3.4129 = 2197.089 Btu : (x 58% = 1,274.31 sensible load, x 42% = 922.78 latent load)


FRESH AIR -

15 cfm/person

Live Room & Control Room - both calculated for 4 people - 60 cfm

Ventilation index from ASHRAE for my city: 1.0 ton annual latent load vs 0.4 ton annual sensible load

60 cfm x 1.0 ton x 12,000 = 720,000 BTU/year for humidity / 8,760 (hrs per yr) = 82.19 average latenty load BTU per hour (does this calc work?)

60 cfm x 0.4 ton x 12,000 = 288,000 BTU/year for sensible / 8,760 (hrs per yr) = 32.88 average sensible load BTU per hour (does this calc work?)


Totals -

Total maximum live/practice room = (3,400 + 82.19) = 3,482.19 Btu/hr latent load, 9264.50 Btu/hr total sensible load = 12,746.69 Btu/hr.

12,746.69/12,000 = 1.062 tons per hour

Total maximum control room = (922.78 + 82.19) = 1,004.97 Btu/hr latent load, 5,574.36 Btu/hr total sensible load = 6,579.33 Btu/hr.

6,579.33/12,000 = 0.55 tons per hour
Old 25th April 2019
  #8
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Anybody with any knowledge/experience with ducted mini-split AC and heat pump units and ducting in unfinished and vented attics? Is it possible with insulated duct work? Any measures to protect the AHU, or specific brand to look at? Any info would be great!

Thanks!
Old 4 weeks ago
  #9
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Looking for a little more info, if anyone here can help out. Please disregard my previous post about placing air handlers in attic. I've since changed my design to have a finished storage/mechanical room from which I will make separate duct access to both the control room and the live room.

My question is: I'm thinking the best way to do this will to have both a ducted air handler for my AC/heat, and also have an HRV to provide the ventilation, and have them "share" the duct work/baffle boxes to the rooms (as Stuart mentioned doing above). I can't seem to find any info on how to integrate that system, as far as how it would physically connect together. Does, for instance, the supply line from HRV hook directly on as the intake of the air handler? Would they be independent and then just connect the supply line from one into the other somewhere before the baffle boxes (if so, where)? Or even just have them almost entirely separate with 2 "inputs" on the boxes, so that is all they share? Any info would be appreciated!!

Also, in regards to that, I'm also wondering if I can get some input (based on my above calculations, or if there are just some standard numbers) as far as what I will need for duct sizes? My control room will be 1,710 cub. ft., and my live room will be 3,192 cub. ft.

Thanks!!
Old 3 weeks ago
  #10
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Quote:
Originally Posted by seandoe View Post
My question is: I'm thinking the best way to do this will to have both a ducted air handler for my AC/heat, and also have an HRV to provide the ventilation, and have them "share" the duct work/baffle boxes to the rooms (as Stuart mentioned doing above)
My understanding is you install it on the return air duct and then the AHU's blower has to run all the time-

https://www.finehomebuilding.com/201...-hrvs-and-ervs

Which begins the interesting dilemma, because the *best* way to install an ERV/HRV is with it's own dedicated ductwork so you don't have to run AHU in fan only mode all the time.

One other thing to look into is in highly insulated studios, if you go fully ducted you will probably want active zone dampers and independent thermostats in each room...5 people rocking out in the live room will need more AC than one person in the control room. Of course if the damper closes, it isn't bringing in fresh air anymore. There are pros and cons then to mini-splts + dedicated ducts for fresh air and fully ducted systems...
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