Heating Estimate

Is this going to be open fronted?

Without details of the insulation levels this is impossible.

Suggest you tell whoever asked you to stop wasting your time with unanswerable questions. (And that's being polite)

Would he get the quantity surveyor in before there is a design?

Is this guy Dilbert's boss?

I totally disagree with you that this is an unanswerable question. I say that because I am not asking for a perfect answer, I am asking for an Educated Estimate.

I apologize for not explaining everything totally, maybe this might help:

A building is being installed in the near future and we have the heating loads and therefore the natural gas loads. We know that down the road, there is going to be another building of size mentioned in the original post near this building. The gas supply main that feeds this building will also feed the future building. So it makes sense to size the gas main for both loads the first time does it not?

We have to have the capability of putting some sort of a number to this without just saying that the question is not answerable and making rude and sarcastic comments.

I totally disagree with you that this is an unanswerable question.

Self evidently you are correct! As an answer can be pulled out of a hat!

However at the risk of being pedantic...

...Educated Estimate...

Hmmm I think by definition..as you haven't been furnished with sufficient information it can't be an 'Educated' answer.

The safest thing is to over estimate deliberately... but if you can't even say if it is an enclosed space or not I stand by my original comment...

I'm not trying to be confrontational or argumentative...I just think your boss is taking the mickey!

Good luck...

Del

Do you realize that you are of no help whatsoever?

I didn't know what you meant by open fronted. I thought: 'The person can't seriously mean that the building is open to the minus 22 F atmosphere in the winter' but apparently that is what you meant. Common sense alone can answer that one but I will confirm that it is an enclosed space.

Okay, lets over estimate deliberately like you say in your post. Now how do we estimate the heat load? If you are saying it can be overestimated, you are saying it can be estimated.

Please only respond in this thread if you have actual helpful knowledge that can be used to produce some type of good or educated estimate. If you are bored and like to pick apart other peoples threads because that makes you feel like you know something, your comments are not necessary.

Do you realize that you are of no help whatsoever?

No I didn't!

I was under the misapprehension that all input would be welcomed, also I know that a thread with no answers often stays that way.

There is obviously some misunderstanding of the term 'Garage' as a commercial building of this sort in the UK could easily be open fronted.

Final my attempts at contrition and humour are obviously also misunderstood.

Maybe someone who appreciates a surly tone will respond, but I somehow doubt it.

You certainly won't hear any more from me .

Del the cat: With over 1600 contribution I've always admired you as the first to bell the cat. However, you've been very rude to poor Paty0 and i side with telesky.

i'm not even 10% compared to you. I still admire you but please, you do owe an aplogy to Paty0. It will not hurt.

Howeto did a very good contribution

PS.

You have variously said 'good' estimate and 'educated' estimate.

I reckon the best you'll manage is a 'very rough deliberately pessimistic' one.

Maybe this will spur someone more gallant than I to contribute !

(C'mon Guys give me a damn good spanking!)

Do you actually have the ability to come up with a 'very rough deliberately pessimistic' estimate?

I have read though all your exchanges and must coment that the tone wasn't quite palatable.

I think what patyo was trying to say is like coming up with a heat balance relationship that will simulate the scenario with the room and external temps. as given.

what has to be played around with here now is material of insulation(transfer coeff.), exit and entry doors(frequency of traffic) and if there's need for heating depending on time of year and stuff like that.

but seriously no precise and very helpful tips can be given if one does not know all the variables.

good luck.

hi,

Took a second look at you question. what you are actually asking about is heat content.

i doubt it the relationship you posted is will surfice.

this will be more like it:

Q = v.d.H.T

where; Q = quantity of heat in room

v = vol of room

d = air density

H = specific heat capacity of air at ambient temp.

T = room temp.(absolute)

be careful with the units as this can throw you out dramatically.

on your second question. its 1,000,000. bcos, k = 1000 and M = 1000,000.

good luck.

You say, "A building is being installed in the near future and we have the heating loads and therefore the natural gas loads." Considering that I understand the sentence correctly, with this information, can't you infer what the future building will need, given that it will be in the same geographic location?

try this gratis

Tac Led

PatyO,

Here's what I would do. I'd find the most correct formula I can, make and document my assumptions on everything and then present my assumptions as "Design criteria" and tell them to build the building to your criteria, if they don't like it, then you can always say it would have worked had you built it to my requirements.

Good Luck

I really thought that this would be an easy one. I guess that it is not.

The reason I say this is because if I wanted to estimate a cooling load for Air Conditioning on a building I would use the 'Rule of Thumb' of 1 ton of cooling for every 400 square feet. And low and behold I would have a pretty good estimate for how much cooling I would have.

Example: 4,000 square foot building would require 10 tons of cooling as an estimate with standard 8' high ceilings. I would double the number for 16 foot high ceilings.

I thought that someone would have a similar estimating ratio for heating. I guess not.

This maybe helpful

www.natresnet.org/conference/2005/presentations/Storer.pdf

And this website

http://www.hvacloadcalculations.com/

Your formula is what is used to calculate the sensible heating of delivered airflow in cubic feet per minute -- and therefore incorrectly being used here.

For example if you had 1000 CFM of airflow that was delivering air heated 30 degrees, the heating would require:

1000 CFM x 1.08 x 30 degrees = 32,400 btuh (btu per hour)

Heating load is based on wall and roof conductive losses to the outside plus either infiltration or ventilation rates.

Infiltration rates are usually defined in air changes per hour. Ventilation to positively pressurize most buildings to avoid cold spots caused by infiltration requires roughly .05 cfm per square foot of floor space -- depending on the tightness of the building.

Assuming 20 foot ceilings, the internal volume is 3,400,000 cubic feet. Assuming the building is loose, being a garage, and experiences one air change per hour, that would be 56,667 cfm.

56,667 x 1.08 x 90 deg dT = 5,508,000 btuh

Heat loss through the walls and roof has to be considered. Assume roof insulation has an R factor of 24 and the walls are roughly 40,000 sq ft and have an R factor of 16. Heat loss through them would be:

170,000 * 90 deg dT/24 = 637,000 btuh

40,000 * 90 deg dT/16 = 225,000 btuh

Total maximum heat load would be 5,508,000 + 637,000 + 225,000 = 6,370,000 btuh

Heat generating devices within the space such as lights, motors, people, etc are not used when calculating maximum heating load. Similarly maximum heating load is assumed to occur at night so solar is ignored.

M as used in Mbtu means 1,000. It is the Roman numeral M for 1,000. 1,000,000 is represented as MM as in MMbtu.

Thank You!

Howetwo is the winner of a gold star!

Everything that I was looking for has been answered, and I can use this information down the road.

I just knew that the human race was capable of providing an educated estimate for this query.

You should be glorified for taking the initiative to use assumtions for R values. This is how people should respond to these queries as opposed to simply saying that it is an unanswerable question.

Well Done!

I almost agree with Howetwo, but being a somewhat swag I think I would add some fudge. Something on the order of 15-25% to cover any surprises when the building actually gets designed. And depending on whether Dilbert or his boss (the pointy headed one!) is using the information, I may or may not mention the fudge.

There should be more time as the building is actually designed to refine this ballpark estimate.

Howeto - U R a Gold Medalist. You enhanced my whatever little knowledge.

I've gotten similar requests like this time after time as a past HVAC designer. It's not uncommon for a builder to come in and ask this question.

There are certainly rules of thumb to use and assumptions can be made to the typical build of that location or you can ask a few questions (levels of insulation, sq. footage of windows / doors, etc).

Being a garage will tell you a typical amount of air changes per hour.

Bottom line is you will need some additional information, but not much.

It would require some more thought and time on my part to be of more help.

I am not a Commercial Building heating guy but an industrial Boiler/Steam Trap specialty & steam piping designing guy. Being a Canadian too, I am aware of the winter temperatures since I faced minus 34. I will try to help you out as:

MBtu = 1000 Btu MmBtu = 1,000,000 Btu

In Toronto Canada you can contact Spirax Sarco at Markhan and request their Practical Study Information Book PS11 on Warm air heating system.

You can also contact Armstrong International direct or their Distributors Preston Phibbs.

Armstrong too has a book as well as a software on humidification engineering & selection. Armstrong also makes Radiators so great help.All books & software are Free.

Now from the book PS11:

For a conventional LTHW heating system:

Load Q = UA t (Q = load Btu/hr)

(U = Heat transfer coefficient)

(A= Area)

(t = Design temperature difference)

For warm air heating system:

Load Q = mCx Δt

Where Q = Load in Btu/hr

M = Volume of air ft³/hr

C = Specific heat capacity – amount of heat to raise 1 ft³ of air

through 1ºF which is taken as 0.02 Btu/hr

Δt = Temperature difference incoming air temperature minus

Desired internal temperature ( ºF )

To determine value of `m' re-arranging formula:

m = Q

_____ = ft³ of air

C Δt

(In practice duct sizes, fans etc., are selected from charts ft³/min of air volume

And so m = ft³ of air/60 = ft³ /min of air

Heater Battery Rating:

Q = ft³ /hr x Δt (Air off – Air on) x C (Specific Heat) = Btu/hr

Calculting Heater Battery but this time re-circulating all the air:

Q = m x Δt x C = Btu/hr

Sorry I amy not have been such a great help but I believe I made a friend in Canada.

For God's sake take that picture of the ass off. Some people may try to take advantage of you.