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OK, so this may be bordering on off topic for the forum, but I reckon it's close enough to warrant some discussion.


Our 250 seat venue suffers, as I'm sure do many others, from a distinct lack of ANY air conditioning. In fact any cooling whatsoever, and an inflexible heating setup.

Over 15 years ago the then chairman of the management committee did a funny handshake (allegedly) with one of his brothers and we got an installed heating system based on a huge block storage heater (100A 3-ph!) with a timer controlled fan circuit. I won't go into the wheres and whyfores of the extreme limitations of this setup - they're rather obvious!


Anyway, the simple fact is that we really need to investigate some sort of aircon to cool the place in the warmer climes and heat it effectively, and on-demand, when it's cold.


Now some years back I had one company cold-call us, so I thought 'What the heck' and invited them to quote for an install. What he described was an externally mounted heat exchanger plant (roof located) with ducting every which way but loose overhead and underfloor of the aud rake. That came out at around £250K - not something I could even entertain starting to think on! Another contractor quoted for a different system, which came out around the same mark.


Anyway, I've recently been getting a bit of spam from another aircon company, pushing for potential business, so I again thought 'Sod it' and had them in today for a different approach.


The guy came over, took the measurements of the aud, and promptly recommended four separate cassette type units, with externally mounted condensers. He assured me that the level of fan noise on these modern units was well below that of units only 5 years ago, and his calculations said they'd cope with the space well.


So, my question - to those with actual experience only, please - is will these cassette type units do the job?


Our space is roughly 21m by 11m, and 7m floor to ceiling, though the top of the raked aud is roughly 3m from the ceiling.

The proposal is to have two 14kW wall-mount units at the stage end, about 1/4 of the way back, and two 10kW units at the rear of the aud.

The standard FoH LX rig consists of a total of 30 to 35 profiles (between 600W and 750W) plus half a dozen Par 64s on each side boom (one each side).

The aud seats 250 when full.


I will most certainly be looking at alternate suppliers for input and quotes, but real-world experience is always good to get.

(I'll also be asking for any local installs where I can get to look at and listen to these units).

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He assured me that the level of fan noise on these modern units was well below that of units only 5 years ago, and his calculations said they'd cope with the space well.

Did his calculations take into account the potential 30kW of heat from the lighting rig, and the 25kW from the audience, as well as any solar gain etc?

So, my question - to those with actual experience only, please - is will these cassette type units do the job?

My experience here is in the IT arena - we use lots of these units, but only for smaller areas - typically 5-10kW. One area has 3 units, supporting about 40kW. They can be very effective, but we've never been too bothered about the noise levels. We've got a few quiet units, but only for small conference spaces. If you want quiet, you're talking about shifting large volumes of air slowly. This is expensive.


However, they can be expensive to run. Do the sums carefully. The most recent system I specified, which supplies a server room with a load of around 100kW, wasn't cheap. But it's a glycol-based system, and we can get "free cooling" - as long as the ambient temperature is at least 3 degrees lower than the set point (which in Glasgow it usually is!) we just run the pumps and fans, not the compressors. Cost more up-front, but lower running costs.


However, that particular system would be less than ideal for a theatre space - the external units are about the size of a transit van, and the internals are rather noisy - and breezy! We've successfully flown a kite in our data centre.....



I suspect that doesn't help too much!

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We certainly discussed the number of lanterns burning up there - one of the reasons for looking at the wall mounted units at the stage end, where the majority of these are.


To be frank, I'm not yet convinced that these will do the job. he's gone away to work out more detail, and to speak with the manufacturers, Mitsubishi, for advice on what their units might handle.


Let's be honest, this is far from your typical comercial/industrial situation. He's never equipped a theatre before, but I suspect it's not something many companies will have done.


I'm really looking for some feedback to say "we did that and it's fine" or "not a snowball in hell's chance, mate".....




A concurrent post has been automatically merged from this point on.


and the 25kW from the audience, as well as any solar gain etc?
More likely 250kW - 1000W per body was always my perception of body heat
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One pertinent question is Aircon or just Ventilation and Heating?


I have just been there, and in the end punted for vent and heating but not active cooling or humidity control (Energy and maintenance costs as well as the capital cost). Cassette units will only cool the air that is in the room anyway, but will not bring fresh air in (which will be a problem).


The Yellow book lists design values for fresh air supply, but as I recall it works out at about 1M^3/s per hundred people which equals largish fans and silencers, be very sure to write a binding acoustic performance specification for any new air handling plant, they are never as quiet as the supplier assures you they will be when bidding the job.


Any warm air system will be expensive to run, so I would strongly advocate trying to have some way to keep the place warm without automatically needing to switch the air handlers on, we put in underfloor heat, but long wave IR powered with hot water might work better for you.


Regards, Dan.

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Good point.

It will, as far as I can see, a closed circuit system - ie no exchange of actual air taking place.

I appreciate that it may well be an expensive option compared to some, BUT the balance from our end is that (if it works) it very likely will be cheaper and more reactive than the big 3-ph storage blocks we have (which more oft than not ADD to the heat when we least want/need it, thus causing further issues!)


We're a LONG way from making any sort of decision and rest assured we'll be looking at various aspects before we do. But as a pretty inexperienced layman on this subject I thought it would be useful to get some idea of what questions I need t ask next - several of which have arisen already here...! :blink:

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Following from Dan's point about forced-air ventilation versus AC, this is the system we use. It has radiators in-line where values are interlocked with recirculation louvres. We have multiple systems to cover different zones, with the largest being 700cap standing with approx 70k generic potential and 8k of movers.


While it is effective in all but the busiest & hottest days of the year, it has its disadvantages: It is very expensive to run (3ph fans individual supply/extract per zone), it is complex and has to be run in order to heat as well as cool.


Wall-mount AC has been used successfully in smaller spaces of our sister venue. I think you might find these will be a good solution coupled with a separate heating system - either modern storage heater or just standard radiators in the auditorium. If necessary you could add some simple extraction in the roof.


Whatever you do, keep it simple. Don't be talked into some clever environment control with all its sensors. Just an AC switch & a thermostat on the wall for the radiators!

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First, the Rolls Royce system. The local theatre here has the entire auditorium rake on a raised floor and the space underneath is a pressurised plenum filled with chilled air. One leg of each and every seat is a duct and a small amount of chilled air wafts out of the back of every seat. Very pleasant when the place is full! FYI, the plenum is also a useful cable route and a pleasant place to work on a warm day! I've never seen this any place else but it works well.


Okay, now that I've spent ten times your budget, some (hopefully) more sensible stuff.


First off, I'm another one who was taught that each human body is equal to 100W of heat...that's what I've used for years and it seems to work.


Like most of the other posters, I've only seen the cassette type units used in smaller areas--however, they are very common down here in substropical Aus. I can certainly comment on the noise factor--the modern ones are very quiet indeed. In fact, as I type this I'm sitting about six metres from our home unit in a quiet domestic lounge and cannot hear the fan. Even when on the highest fan speed, the noise is only barely perceptible at this range. I notice that the spec in the instruction book gives SPL details for both the indoor and outdoor units so noise should be something you can get an accurate fix on.


I'm certainly not automatically against the four x cassette unit plan. Although not as elegant as the all singing, all dancing solutions it could well work. Have four separate boxes even gives you a rough and ready way of "scaling" the system. Run one box when the theatre is dark, two for rigging and lighting days and the whole shebang when the audience is in. However, I have to say that 4 x 14 kilowatt sounds underspecced to me...perhaps just about enough to cope with the lighting and audience but not nibbling into the background thermal load. It might be worth asking to see the assumptions in the calculations. It's also worth saying again that these cassette units just recycle the interior air...you have to look to other means for ventilation and fresh air (which, in summer, can add to the thermal load.


One other point: are you thinking of adding some cooling even in wiinter when the audience is in and the lights on? If you feel you need this, check the operating range for the condensor units. These can assume a relative warm outside temperature as the minimum they can operate in....fine in an office or domestic setting but perhaps not with the weird and wonderfullly varying loads of a theatre.


Hope this helps.



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I'd really want to see his calculations. 48kW of air-conditioning will not remove 48kW of heat load from an occupied space. My background in this area is TV studios and my first reaction on seeing your post was - 'far too small'. Somewhere I should have on file copies of designs drawings and quotes from the last couple of jobs. It'll be next week before I have time to dig them out but I'll take a look.
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One of the theatres I've worked in has just had aircon put in. They have 4 split system heads with external condensers (can't be sure of the sizes, they look about 10kW each but the theatre is about half the capacity of yours) they handle the heat that we get here in Perth quite nicely.


Slightly OT, in these parts most people would refer to a reverse cycle aircon with an external remotely located condenser as a split system whereas a cassette is a type of split system that is mounted in the centre of the cealing rather than on a wall. Is that just a local anomaly?


Some other thoughts:

* The split system aircon that we have at work has an optional fresh air duct that brings in a percentage of outside air.

* Discuss the difference between inverter models and standard ones. The inverter units slow down rather than cycling on and off.

* Make sure you check your available incoming power supply early on in the piece.

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I have considerable A/C experience but confined to large shops and office buildings, not theatres.


If you need precise temperature control, adjustable in different areas then a relativly expensive system will be required.

If on the other hand you simply wish to make the space "less hot" then simple equipment of adeqaute capacity will do.


The main factor to consider is do you wish to cool the air already in the space? or do you wish to cool outside air, and blow it into the space?


If the building already has an air handling unit that supplies fresh air via ducts, then adding refrigeration to this unit is probably the best option.


If no such AHU is installed, consider if one should be fitted, complete with cooling. This system has the advantage that the fan only can be run when its cool outside but hot inside, the energy consuming compressor(s) only being run when the outside air is too hot to achieve any cooling.

The fan should idealy be variable speed.


If no AHU is installed, nor likely to be required, then consider split units as first suggested.

Such equipment cools the room air, but does not normally supply any fresh air.


It should be noted that A/C equipment has two ratings, both in KW. One rating is the electrical load in kilowatts, the installing electrician needs this to correctly size cable etc. The other rating is the cooling output also measured in kilowatts, this figure is needed to correctly size the equipment.

Note that the stated cooling output is often under ideal conditions and seldom realised in practice.


In theory one should calculate the heat to be removed, in kilowatts. This done by adding up the heat input from the lighting rig, the body heat from the occupants, the heat infiltration from the outside, and any other heat sources, plus a margin of ignorance.


In practice I would simply add the load in KW of the lighting rig, and an estimate of body heat, and size the units on that.

Consultants will (for a large fee!) produce a detailed plan of what is required, another consultant with the same information may produce a quite different result.


A lot also depends on the building construction, substantial thermal mass (lots of concrete or masonery) is easier to cool.

Somwhat undersized equipment may in fact give satisfaction since the performance is only for a couple of hours, unlike say a department store open for 15 hours a day.

If the space temperature rises from 23 degrees at the start of the performance, to 25 degrees at the end, this may be acceptable, whereas the same rate of rise if continued for many hours would not be acceptable.

The great advantage of a number of split units, is that additional ones may be added later if required, upgrading central A/C plant is more of a challenge.


Also take every oportunity to reduce the heat produced in the space to be cooled, any lamps that are permanetly dimmed should be replaced with lower wattage ones for example. LED lighting should be used where possible.


Finally make certain that you have enough power available ! if useing A/C will take you near the limit, consider having an electrician install ammeters on the intake, in order that the current used can be determined by simple observation rather than redious calculation (or gueswork!)

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and the 25kW from the audience, as well as any solar gain etc?
More likely 250kW - 1000W per body was always my perception of body heat


The generally accepted ballpark figures are 100W per body sitting idle, 200W for light work and 500-1000 for strenuous exercise. I suspect your audience will be at the lower end of the range.


The design should also take into account the humidity and moisture emitted by these 250 bodies...

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In todays eco friendly climate surley we should be trying to use less energy,so may I suggest a solution that was in use for many years,long befoe electrickery was discovered ,personal A/C



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we have a hall almost the same setup as yours, and can say (from the same amount of air con power as proposed) it will not cut it.


we have had ours flat out all evening for a music BTEC FMP, and it only took the edge off the heat, and it wasnt even that warm outside.


we have had running 4x 575 movers, and generic lamps to total approx 15K


we have 4 of the mitsubishi units with external heat exchangers on, also this was music event, so they could be on full, for a musical, 1/2 is the most you can use them and not be too intrusive on noise.

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  • 3 months later...

OK - still on this little project...

Had another quote from a more local company last week (funding requests always dictate at least three quotes).

This one did an install at the Arts Centre (Artrix??) in Bromsgrove.


Any Blue Roomers from that neck o' the woods...?

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In our smaller venue, which is a max capacity of 250 standing, we had a tempered air ventilation system installed last year.


It doesn't chill the air - so in the summer months it just pulls fresh air in from outside (via filters). In the colder months, the air is tempered by passing through a radiator which is connected to our central heating system.


I was sceptical last summer that it would work, but this summer is turning into a scorcher and it is performing very well - It always feels "fresh".


The system feeds the air into the room via standard ventilation ducting and because the fan/motor is back close to the inlet, all you hear in the room is the rustle of fresh air!


This system cost about £15k installed.

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