Selection Opinions.

[Daddy Cool]

i'm seeking opinions on what should just be straight forward budget pricing, but the more i look at it, the problems it's throwing up.

The air is approx 25m long, by 8.5m deep. O/all height is 2.7m ground floor and 2.8 for the mezz floor. (mezz is basically same size)

The front is all glazed, no shade or blinds etc and faces SW.

Space for plant is very limited on the roof, and i need fresh air at 12 l/s for 200 people.

Having done several methods of calc, they are all coming out bigger than the last, mainly solar from the windows and gain from the supply air.

I want to use outdoor ambient of 33c, maybe 35c to be safe.

Anyone got any feeling for total UK duty?

[rbartlett]

The glass is an obvious way of solving this.

Remove a pane at a time block out with plywood and replace with a window rattler. This will have a duel effect as it removes heat with the rattler AND reduce solar gain by removing the glass !!

keep doing this till you reach the temperature you require everybody's happy;-)

I'll get me coat....

Cheers

Richard

[Daddy Cool]

I'll get me coat....

Bit hot for that isn't it?

[al]

if you're ducting in fresh air would a 25kW rooftop not suffice, or have i miscalculated......

Al

[rbartlett]

if I read it right. You're looking at 150+kw depending upon the things I don't know

either way if there is such a glass wall they will end up shading it as people will not be able to work at p.c's etc

the temp will need to be kept 20 or below and the air should have a high movement to reduce the feeling of the sun -bit like when you drive in the car

cheers

richard

[frank]

if you're ducting in fresh air would a 25kW rooftop not suffice, or have i miscalculated......

Al

Hmmmm

200 people at 90w sensible = 18kw
200 people at 50w latent = 10kw
200 people at 12 l/s (t1 -t2) (35 -21) = 58.13kw
Lighting = (25 x 8.5 x 2 x 15w/m2) = 6.38kw
Solar = ?
Fabric gains = ?
Infiltration = 3.93kw based on 0.5 air changes per hour
Equipment = ?


25kw might be a tad undersized

[al]

no wonder my stuff never works........and i thought it was because it was LG

[Daddy Cool]

either way if there is such a glass wall they will end up shading it as people will not be able to work at p.c's etc

Sorry, not enough detail from me, they want to turn the building shell into an art gallery. They have suggested exposed cassettes or ducted fancoils.

I hope it's modern art, so i can just throw the stuff in, have it look like a dogs diner, and call it 'Art' might even be able to sell it onto the Tate Modern if i call it 'Twisted metal of my fried brain' and call my self 'Sergio the tortured' (apologies to anyone called Sergio the tortured

i'm getting just over 200kW at design temps, but don't currently have enough room for that much equipment, looks like a new plant room coming.

[Jez]

I think that you need to be a bit more realistic.

Is it likely that the gallery will have an occupancy of 200 people when the ambient temp is 35°C? I would imagine that a gallery gets the most busy in the evenings (for shows etc.) when the ambient temp has dropped considerably. I would also guess that 200 people does not occur every day.

The AHU should also have some sort of heat recovery function between extract and supply (usually about 75% efficient). This will reduce the amount of AC plant accordingly.

[Daddy Cool]

Hi Jez,

I fully accept the sensible factor, and heat recovery is a must. i personally feel it's for the client to factor in the variables of how many people and when. to be fair to them, it will get a lot of use both during the day and evening.

i'm always very cautious about doing too much factoring on the clients behalf, i've been caught out before, and as such always state my design conditions for them to approve.

[Jez]

It's always good to discuss it with them. They may be looking for guidance and are unsure themselves.
You could always do a selection for 'worst case' and 'likely case' and as you say, state your assumptions for each option.

[Daddy Cool]

I take your point Jez, maybe i'm just tired of the 'i want the best duty for lowest price' rather than best option.

Mentioning no names, i decided to ask a manufacturer to do some calcs and selections, earn their money. well having lost three days, it was all wrong, cassettes rather than ducted, no central control, and having done an AutoCAD drawing of the site and plant area, i asked how they propose to have VRF condensing units with 20mm clearance all round???

Give up

Any suggestions of a manufacturer who doesn't just give you the manuals and has an ounce of common sense?