Heat load

[Peter_1]

Visited today a customer (restaurant) who installed recently a new dining room.
Dimensions: +/- 12 x 20 x 3,5 m (+/- 36 x 60 x 10 ft)
Place for 250 sitting persons or 150 while dancing.
But.... when I entered, temperature was already +/- 40°C on 11 AM.
But now the clue, the roof is made of a 3 layer polycarbonate plate (with a U value of 2,1 according to the owner)
The plates are opaque, no other sun protection.

I did a quick calculation which gave me +/- 115 kW, needed air volume for this +/- 22.000 m³/u or an air change of +/- 25/hour.
This seems almost impossible..

Any suggestions or corrections?

[chemi-cool]

Hi peter,

Iv'e seen on TV its getting hot your way How many AC's do you have at home?

My suggestion - go away from there, if there is direct radiation of the sun, you can not calculate it.
Ask the owner to install a proper insulated roof and call you again.

chemi

[Abe]

At college they told me the suns energy is increased, radiated plus 80% through a glass roof.........

So Chemi is spot on...........

I would not dream of quoting with confidence any area which receives direct sun input through it

[Peter_1]

Thanks guys.
Aiyub, your avatar is gone
It's indeed very hot but I think these temperatures are rather normal for Chemi in teh Israeli dessert.
In the shadow, I measured this afternoon 35°C.
Serviced this afternoon a compressor with a condensor pressure of 28 bar, liquid was +/- 45°C to 50°C.

That's also what I told the owner already but somebody else gave an offer with a Daikin VRV of 22 kW. I estimated a heat load of 100 kW.

[Andy W]

I reckon on about 98.7 kw, I would do the job but insist on blinds for the ceiling and some knid of extract at the highest point to occassionally take away excessive hot air if a pitched roof.

[Brian_UK]

Or they could add a permanent water feature on the roof to provide heat removal !

[rbartlett]

forget load -go for budget

ask him how much money he's got to spend on this and proceed from there..


cheers

richard

[chemi-cool]

Last year, I installed a 35 Ton package for a dining room where some 350 people are eating lunch.

I have told the designer that some of the windows are letting sun rays entering the place and heating part of it.

He said it is nothing, and it was a disaster.
Eventually we added shutters on the outside of the windows and all went fine.

35°C in the shade? in Belgium? Serves you right, why should we get all the heat?

This is normal temp out here until September.

Chemi

[Andy W]

forget load -go for budget

ask him how much money he's got to spend on this and proceed from there..


cheers

richard

Now that is a good point, how many times have you wasted valuable time to attend site surveys only for when you get there "I thought it would only cost a few hundred pounds".

[chemi-cool]

Money is not the issue here.

Excellence of service, is!

Chemi

[piston broke]

I agree, if you are going to do a job do it right. Those who sell things just for money with no thought about the application make it hard for the rest of us.

They should do us all a favour and go and sell life insurance.

PIST

[rbartlett]

Money is not the issue here.

Excellence of service, is!

Chemi

I've never had a customer who didn't think money wasn't an issue

It's pointless telling him 100kw or nothing. This isn't excellence of service it's arrogance



Cheers

Richard

[chemi-cool]

So we disagree on something,
Friends?

Chemi

[rbartlett]

we are not actually diagreeing -mearly attacking the same problem from a slightly different angle.

I remember years ago talking to a MD of a big multinational about a/c for their HQ.
he actually said "I don't care about the cost I just want the best"
The quote came back at 27k for 7 cassettes. (back then you could charge decent money for a/c;-)

He then "err how about some portables?" so we sold him 7 portables instead..

sadly life sometimes gets in the way.......

cheers

richard

[chemi-cool]

OK,
I just refuse to do jobs when I know that I will be blamed for the results, one recent example:

I gave a quote for a new supermarket, because of the way the building was built, it was possible to hide an AHU and to cool the 350 Sq/m by 6 m high without any ducts + fresh air suplly and using cool air in the winter to cool the place from all the heat of fridges inside.

It was of course more expesive compare to splits.
I was asked then to make another quote using splits this time.

I refused and left.
12 big splits were installed some 4 M high, nobody cleans the filters, no way to know which is working and which is not, water drips on machinery, computers and ptoducts - A mess.

My name and reputation are as clear as the blue sky outside.

This is our disagreement.

Chemi

[rbartlett]

OK,
I just refuse to do jobs when I know that I will be blamed for the results, one recent example:

I gave a quote for a new supermarket, because of the way the building was built, it was possible to hide an AHU and to cool the 350 Sq/m by 6 m high without any ducts + fresh air suplly and using cool air in the winter to cool the place from all the heat of fridges inside.

It was of course more expesive compare to splits.
I was asked then to make another quote using splits this time.

I refused and left.
12 big splits were installed some 4 M high, nobody cleans the filters, no way to know which is working and which is not, water drips on machinery, computers and ptoducts - A mess.

My name and reputation are as clear as the blue sky outside.

This is our disagreement.

Chemi

I don't see it quite that way Chemi

That is a result of poor maintenance not poor installation.

poor maintenance affects all jobs from the 'best' to the 'worse'

Personally never having seen the job but if I had installed those cassettes and they worked but the customer won't have them maintained then I would feel my reputation was 'clear blue sky' too

all our customers are offered a maintenance contract and the need for regular maintenance is strongly advised soIf they didn't work on day one then -yes I agree it would reflect badly but 2 months down the line problems arise because of dirty filters -sorry pal not my fault.

cheers

richard

[Peter_1]

What i will propose to the customer:

Proposal 1: he installs +/- 115 kW so that he can cool the place all the time to a decent level. He's also aware of the fact that the huge ventilation can causes drought and noise. I was thinking also on the cotton ventilation socks because the place is only 3,5 m high. We installed them many times in the Carrefour supermarkets.

Proposal 2: he installs a new roof or installs a qualitative exterior sun shading so that heat load reduces. The costs he saves on the airco can be used somehow for the sunshading shield. Still needed +/-60 kW.

Proposal 3: he installs a reduced capacity whatever he wants but he signs on the forehand a paper that he's aware of the fact that capacity is insufficient to cool the place under all conditions, especially on those sunny days where you need it the most. He will also sign that a much bigger capacity was initially offered but that it was his own decision to install a smaller capacity.

Proposal 4: he rents temporarely professional airco to determine the needed capacity so that he can see for himself what capacity he needs.

I will not accept any other proposal or a mix between these 4 and I feel well with all 4.

[chemi-cool]

Sorry Richard,
You misunderstood me.

The bottom line of what I am saying is that it is wrong practice to control the air in a supermarket that size with products in open cases without air changing at all, no proper way to control temp.
Only looking at the price.

I just don't do this sort of jobs.

If you want it done good - I'm your man.

If you want it cheap - I'm not.
As simple as that.

Chemi

[Temprite]

Proposal 3: he installs a reduced capacity whatever he wants but he signs on the forehand a paper that he's aware of the fact that capacity is insufficient to cool the place under all conditions, especially on those sunny days where you need it the most. He will also sign that a much bigger capacity was initially offered but that it was his own decision to install a smaller capacity.

Some people will just not be told.

If we do a quote and the person takes it on their own back to go for an undersized system.It is always sent in writing to them that it was their decision not ours.

Reminds me of a job we took over after previous mechanic left halfway through.
The builder normally would use Daikin units but decided to buy Masake units himself instead(about 25 units).About half the units had already been piped up with the wrong size piping by the previous installer.The pipe runs were all about 3 times the maximum pipe length. Most of the pipe ends were not sealed at all.When I pointed this out the builder wasn't keen on having all the piping ripped out.So I made him sign paperwork stating that we were in no way responsible for any problems associated with this installation,which he did.
Suprisingly enough all the units actually worked.

I can understand your opinion though chemi.Sometimes it is better to walk away from a job than have your name associated with bad workmanship. Everytime that someone asks who installed the system you know what they will say.

[chemi-cool]

I can understand your opinion though chemi.Sometimes it is better to walk away from a job than have your name associated with bad workmanship. Everytime that someone asks who installed the system you know what they will say.

Right!

Chemi

[rbartlett]

did this one go anywhere??

cheers

richard

[manishjha]

please provide easy heat load calculation format in excel sheet.

Manish Jha

[Magoo]

Rename the restaurant "sauna with foöd " speedo's and bikinis necessary.
magoo

[Makeit go Right]

Just a couple of ideas in case you are able to lower the calc cooling load:
a) At the design peak load (afternoon?) are the 150 dancers dancing already, or does that normally occur in the evening (when it is a bit cooler outside)? Ie at peak load in the afternoon, perhaps the customers are normally just seated, eating their lunch.
b) Are you able to apply some diversity to the customers? Ie is the restaurant always full to capacity at the time of day when the peak cooling load occurs (afternoon?). Maybe it would be sensible (excuse pun) to design on say 75% occupancy (185), or even lower, on the basis that when the place is maxed out (rarely) one would expect the room temp to climb a little outside the design temperature zone.

You have to discuss ways of reducing the solar heat load, of couse. Solar film can be rather effective and practical (go for the max reduction).

[Peter_1]

Original post is already from 2005