View Full Version : Calculating heat load

07-02-2003, 11:13 PM
Is there an easy way to calculate heat load , or selection of compressor/ condensing unit

Say the following.

Cold room size 40 foot x 12 foot x 8 foot high
Temp required -25C
Refrigerant R 404A

Product General produce

I am looking for an easy / rule of thumb method. Nothing too technical

08-02-2003, 10:52 AM
Hi, Abe:)
there probably is no short cut other than asking your wholesaler to do the calculations for you (Dean and wood will). You can cross check their figures by watt per m3, large deep freeze stores can be calculated on 70watts/m3 as a check, smaller stores will need quite a larger wattage per m, this is something you will have to trial yourself.
Regards. Andy

09-02-2003, 06:13 AM
Let's not forget http://www.keepriterefrigeration.com/calcrite/RTcalc1.htm

09-02-2003, 06:34 AM
Cold room size 40 foot x 12 foot x 8 foot high

I am guessing 16,000 Btu/hr. Am I close? I came up with that answer by feel. Not a rule of thumb. And I didn't consult anybody or anything. For all I know I could be a mile off target. But....

I have to think your question points to the need to make quick decisions in front of people.... winging it. Many will say it is bad practice to do so, but more buying decisions are made this way than by thorough methods. Bad practice is an important component of an imperfect world. If one is to commit bad practice, one must be good at it.

I differentiate between "rules of thumb" and "feel." Feel means you have an instinct born of experience. Rules of thumb imply you can imitate feel.

I cannot wait to see how close I was on your example problem. Of course, now I am thinking that it more like 12,000 Btu's, but when I guess at stuff, I know I should pad it a bit.

This is definitely not a proper way to do load calculations.:)

09-02-2003, 06:59 AM
Well, it appears I blew it. I ran heat calc and it tells me it should be about 24,000 btu/hr.

So much for feel, so much for rules of thumb.LOL!

09-02-2003, 10:40 AM
This is what I have been advised by one bloke

Room Volume
40 x 10 x 8 equals 3200 Ft cube

Multiply by Temperature difference
Therefore taking ambient of 40 C less minus 20 equals 60 ted
3200 x 60 equals 19200 Btu

Multiply by 24 hours
19200 X 24 equals 4608000

Running Hours
Divide by 18 equals 256000 btus

Duty for room for condensing unit based on running 18 hours per day is 256000 Btu

09-02-2003, 05:33 PM
Heatcraft has an "Engineering Manual", Pub. #H-ENG-1 (1990). It has a "quick selection chart", from you you selct by room dimesions, room temperature, and heavy or normal usage.

A -10degF room, 12'x20'x8' is indicated as (13599btuh X 2) 27,198 average duty, (28524 x 2) 37,048 btuh heavy usage.

Most of your load is usually latent infiltration which is dependant on the outside (of the room) ambient, and the construction (insulation) of the walls.

Using load calc software in rooms as large as this can also lead you awry. If you do not interview the customer as to actual usage, the default product loads in software can cause you to way over rate the load, and put you out of the running in the price department. Then again, if the customer is going to use the freezer for a blast chiller, and put 170degF baked turkey legs into it in 100# batches....... well then your toast there too!

Even if you go to your wholesaler to figure it out for you, you need to offer some basic information, which you will have to get from the customer. Collect the information pertaining to worst case (highest load) scenario.

(1) What product are you storing?

(2) What is the largest load (in one day) that you will have entering the box. (figure it out in pounds). How is it packaged?

(3) what temperature is the product entering at. In the case of a freezer store, even if it is coming in at zero (presumeably), at least a 5 degree pulldown is calculated, which gives some additional safety factor at least.

(3) determine the highest anticipated ambient temperature that the exterior walls will be exposed to. Indoor or outdoor? (the ceiling temperature is usally adjusted for attic space temperature or exposure to sunlight).

With this information, then box construction and configuration is taken into consideration in determining infiltration (k-factor) in addition to product, personnel, motors, lighting, etc. Each of these have rules of thumb themselves!


10-02-2003, 04:28 AM
Dear Aiyub,

There appears to be something wrong with the last part of the calculation :

Your friend is assuming 1 air change per hour (thats fine!) and therfore you will get 19,200 Btu/hr

Now , 19,200 Btu/hr x 24/18 = 25,600 Btu/hr (not 256,000 Btu)

Note that Dan came-up with 24,000 Btu/hr ( so your friend's method is not so bad after all)

My computer programme came up with 27,255 Btu/hr. I'm contemplating putting it on a PDA application where refrigeration personnel can come up with quick and accurate load calculations on the spot !

Compressor : Bitzer 4CC-6.2 Y

10-02-2003, 02:59 PM
Are we assuming 4" polyurethane walls?

Abe, would you like my "cheat sheet", or are you able to get heatcraft literature?

10-02-2003, 07:43 PM

Sorry I made a typo error.........it is 25600 Btu. Very close to dan's
So looks like this " cheat" method isnt bad at all. Yes, I would like a copy of your sheet

10-02-2003, 07:48 PM
Sorry, I meant Bersaga........
Hey this computer prog of yours isnt too bad
Whats PDA ??
next question.........How do I get my greedy paws on one!!!

11-02-2003, 02:11 AM
Dear Aiyub,

'Mark' is not such a bad name either!

PDA stands for Personal Digital Assistant - it's those thingys that some folks call ' palmtop ' ! Basically a mini PC and there are lot of softwares written for these applications.

Now, my programme is quite a detailed heatload software and is written in Visual Basic and currently I'm getting an application package done for it - converting it into CD's but putting the necessary software locks into it.

When that is ready, I would try to put on the RE forum and allow anyone in this forum to use it and give my constructive feedback.

After that , this programme will go commercial.

Meanwhile, funds received from the prvious will go to developing a heatload calculation for PDA application.

PDA's are quite cheap these days. And for a refrigeration engineer/technician/mechanic it is quite useful to have information on your fingertips :

1. Full Heatload calculation ( interview your client on the spot and ask him all the difficult questions i.e. door openings, product incoming per day, incoming product temp/type , PU or EPS etc. )
2. Equipment selection : this depends on how many manufacturers have their selection software written for PDA's ( Palm OS or Java)
3. Pipe sizing ( as in 2)
4.Costing - you can transfer your current costing spreadsheet into a PDA and produce pricing on the spot for a potential request.
5. Refrigeration Handbook - you can down load refrigeration troubleshooting manuals and handbook into your PC and channel them to your PDA

The potential is great and I would appreciate any feedback on this idea.

Of course, all of these are just tools to get things accoplished efficiently and effectively but is NO substitute to real experience and instinct that is built-up over years and this is what I can see most of the moderators and contributors to this forum have.




12-02-2003, 01:20 AM

You mention a palm top. What an excellent.............instrument for our business. I look forward to testing out this software. Palm computers are the way to go...........I reckon

13-02-2003, 03:10 PM
Hi Marc !

Great work ! What language did you write your PDA software on ?


13-02-2003, 06:02 PM
Morning Marc

Thanks for the supper mate. It was good to catch up again. Hope your brother wasn't too bored!:D
I was impressed with the software - it's exactly that sort of thing that makes PDA's so useful to us tech's.
Aiyub, this software of Marc's is exacly what you need here.
At the end of the day, however, there is no 1 right answer in fridge design. Just about any system will work to some extent. The challenge is designing a system that will achieve what you want, without costing a bomb in installation or running costs.
I remember in college that even with the same question, containing the same basic data, we all used to come up with slightly different answers!

13-02-2003, 09:18 PM

In a word.............Youre a star!!

Thanks for the e mail
I checked it out and its great

Its good to know that when the good Lord was dishing out brains some people, ( like yourself) went and got a good measure
Me I was hiding somewhere and missed out

And you can rest assured, the file is safe with me, ie: if anyone is even remotely thinking of getting it from me.........you will have to shoot me first, even then I doubt you will find it!!!

Yes, I know, its hard to find men of intregity these days, but then I was brought up in time and place when values meant something, and teachers were respected, and occasionaly we got six of the best, and it hurt too.

These days its the other way around........

Am I deviating..........going off on a tangent?? Heck I must be, ok, ahem........Next question, Im looking at the Mitec Mio PDA........ .but not knowing too much about these clever little gadgets I would benefit from knowing which is the best one to go for!!


14-02-2003, 03:12 PM
Hi Aiyub

I thought that I knew most of the PDA's out there, but I've never heard of this one. Is there a website?
Personally, I would suggest that you go for one made by Palm, since that's what Marc has developed the software for, or one of the other PDA's runnning Palm, such as the Handspring or the Sony series. You don't need to have a colour screen, but if the price is right, it does make a big difference. Get one that can take memory cards (As that one of Marc's can), as that gives you flexibility, as well as some degree of 'useful life expectancy' improvement. You don't want to find that in a year or two, your PDA can't keep up!
With that in mind, always buy the best you can afford, as it won't become obsolete as fast.
The only drawback of the Palm O/S is that you need 'conduits' to transfer Windows files to Palm files, & vice versa. However, put 'Documents To Go' on your Palm, and you're sorted. Most of the Palm PDA's will have this software bundled as part of the package.
Basically, I suggest that you go to John Lewis (my local one has a wide variety on display, that you can play with) or P.C. world, and take a look.

14-02-2003, 07:46 PM

The Mitac ones on offer with www.evesham.com
At 199.00 inc vat. Details on their site. But I heed your advice, going to do the rounds, PC world, Dixons, etc and go look and play around

11-11-2003, 09:43 AM
I also a PDA (Compaq) for basic calculations, mostly written in Excel.
Sometimes to do some conversions.
My complete telephone book is stored into it.
My complete pricelist.
All my appointments are stored into it because i'm becoming to an age where sometimes (more and more) I forget something (always thought that this was something for real old guys)
But the most of all, i use it as an GPS (Destiniator or TomTom) while doing different maintenance jobs.

11-11-2003, 09:47 AM
Aiyub, try www.isobar.be. They have a free cold room selection program.
Have also a look at http://www.hvacware.net/engrproj.html not realy refrigeration but interesting

11-12-2003, 12:41 AM
Hello I am really nbew here but if dont have it you must try it,the ccolpack1.46
have a nice day Gunnar Lohse

11-12-2003, 04:11 AM
I find the Coolpack gives much higher heatloads than what is really required - probably a much higher safety factor . Anyone care to comment ?

19-07-2006, 07:57 AM
I am from mideleast K.S.A
Gentile man do you know any easy methods to calculate heat load for cold room
With Regards

21-07-2006, 10:22 AM
as per my calculations and experience you should go for 18432 btu/hr x 2 units at an evp temp of minus 30 deg C. Assumed the average product and average loading conditions.

21-07-2006, 10:27 AM
I am from mideleast K.S.A
Gentile man do you know any easy methods to calculate heat load for cold room
With Regards

:) Dear Rajeev

Nothing is easy and shortcut.

if it easy, it comes by experience and may very from person to person.

You may specify your specific application if it is there.

29-07-2006, 09:46 AM
Keep the insulation about 0,4 W/m2C. 150 W cooling for every m3 volume will be enough.

Samarjit Sen
14-08-2006, 11:10 AM
For calculating the heat load for a Cold Room, there are factors such as the Product to be stored, Incoming Temperature, Cold Room Temperature and wall, ceiling and floor insualtion materials and thickness has to be considered. The best way to go about it is to get a Software and feed in the above datas. There are a number of Softwares available and I would reccommend you to down load the same from www.russellcoil.com (http://www.russellcoil.com) or request for a CD Rom at www.heatcraftrpd.com (http://www.heatcraftrpd.com).

With best wishes, Samarjit Sen

Samarjit Sen
15-08-2006, 02:24 PM
The best way is to either directly down load the selection software from www.russellcoil.com (http://www.russellcoil.com) or request for the software from www.heatcraftrpd.com (http://www.heatcraftrpd.com). These are very easy to use and I presume your purpose would be attained.

Samarjit Sen
20-08-2006, 05:19 PM
Hello Abe,

Have you been able to get the Heat Load Calculation for the Cold Room. If not, could you please intimate the product and the quantity to be loaded at what incoming temperature. I will work out the detail load with the unit selection for you should you desire.

With best wishes, Samarjit sen

Samarjit Sen
23-08-2006, 11:14 AM
Hello Abe,

In case you have not as yet got the heat load for your walk in freezer the same should be 28598 BThU/hr with 18 hrs run time at -30 Deg. C Evaporative Temp. I am also attaching the Load Details for your reference.

24-08-2006, 07:40 AM
[quote=Dan]Let's not forget

Thank you very much for your information.
It's really a good tools.

24-08-2006, 10:17 AM
Hello Abe,

Have you been able to get the Heat Load Calculation for the Cold Room. If not, could you please intimate the product and the quantity to be loaded at what incoming temperature. I will work out the detail load with the unit selection for you should you desire.

With best wishes, Samarjit sen


Thank you for your assistance. Unfortunately that project fell away.

Best Regards

21-11-2007, 09:19 PM
the grainger catalog has a page for btu calculations, but im not sure if they go that large

05-01-2008, 02:13 AM
a rule of thumb option, is to calculate outside surface area in feet squared and multiply that by thirteen low temp, by sixteen chiller range (Btu's /hr )They get you in the region of actual for a budget price, do actual calc on specific application to double check loadings. on info earlier posted the load would be 23296 Btus /hr.
Cannot remember the SI factor for metres squared.

cheers Magoo;)

Guy Booth
07-04-2008, 06:47 PM
I'm seeking a coil selection program to help select coils that will perform in air handling units. Often when selecting an air handling unit there is rarely data readily avalible to schedule pressure drop information. i.e. air pressure across the coil as well as water pressure drop. When scheduling these pieces of equipment it is essential to have this particular information so that fan statics and pump head calculations can be completed. Would anyone happen to know where or if the program exist?.

08-04-2008, 04:12 PM
hi everybody how can we calculate spacific heat of flowers vegetables & fruits.should spacific heat & respiration both be taken in considration for heat load calculation.

Samarjit Sen
08-04-2008, 07:01 PM
Yes while calculating the heat load, one has to consider the specific heat, latent heat and respiration. In case you get these datas please share with me.

08-04-2008, 10:50 PM
Just look in the back of the HRP catalogue cmon guys it aint rocket science ???

08-04-2008, 11:30 PM
Just look in the back of the HRP catalogue cmon guys it aint rocket science ???

Not everyone on this forum is from the uk so i doubt if they have a hrp catalogue.

You could always print it off and upload it for them;)

Samarjit Sen
09-04-2008, 03:53 AM
Hi Guy Booth,

It appears that you are looking for coils suitable for Chilled Water Coils for Air Conditioning applications. Most of the coil selection programmes do not give the pressure drops of air or water. They will specify the coils model of their make. For getting the pressure drop you have to work it out your self. However you may check the CoilPro of Colmac Coils.

Samarjit Sen
09-04-2008, 03:55 AM
Hi Shabbir,

The information sought by you are available in the Post Harvest Books and also on the Engineering Tool Box web site. For further information you may PM to me with what exactly you are looking for.

Samarjit Sen
10-04-2008, 06:01 AM
Are you looking for these attachment.

10-04-2008, 06:21 PM
thankyou samarjit sen for the attachment it willbe very helpful I still need specific heat data of flowers for flower cold storage.Ialso would like to know how to calculate heat load using specific heat letant heat & respiration data.I would like to have calculation formula using all data.

Samarjit Sen
11-04-2008, 01:52 PM
Hello Shabbir,

I presume that you are a refrigeration engineer and as such should be aware of how to calculate the heat load.

I am much elder to you and for your welfare, I would advice you to please study the various books and also go through the forum. Refrigeration line involves a lot of study and we all have come up the hard way and are still learning. Heat load is a very basic thing. I remember there was a post by an Air Conditioning Consultant asking for heat load calculation and how it is to be done. He was also from India. It is sad that we do not go into the basics, but try to know much high. It will not help you. Please take my advice and do a little bit of study and practice. There are lot manymembers in this forum who are of immense help, but first you have to try your self. The forum is meant for this and you will get a lot of help.

Sorry for the lecture, but I just could not help.

11-04-2008, 03:56 PM
I still need specific heat data of flowers for flower cold storage.
Rule of thumb for flowers:

Product BTUH load = 20 x box length(ft) x box width(ft)

This rule is only valid for storage boxes. If the flowers are entering directly from the nursery or field you must calculate the heat of respiration.

I also would like to know how to calculate heat load using specific heat letant heat & respiration data. I would like to have calculation formula using all data.

I suggest getting hold of an engineering manual from one of the manufacturers such as Heatcraft, Keeprite, Russell etc. Then make copies of their blank load calc forms and practice running loads using their tables and data.

Then, after you have a good understanding of the process to run loads properly using the manual system, switch to a computerized version.

I perform about 1400 load calcs a year average.(sorry about the boasting, just trying to make a point) I recently trained someone to help me and I didn't let him use a computerized program for a year.
Once he did he was very good and was able to catch any mistakes due to incorrect data.

Finally, I always perform and print a load calc on all jobs. Let the customer see this and sign off on the data inputed. This is the way to find mistakes and correct them before the job is installed.

Samarjit Sen
11-04-2008, 04:34 PM
Hi Powel,

I feel bad having to say a lot to people like Shabir. They come to the forum but want that everything should be spoon fed to them. Heat Load is a basic in refrigeration and air conditioning. First you ask for the Sp. Ht. and then you want the heat load calculation. As you know as to how much hard work we had to perform, before we learnt a bit. Why cant these people at least make an attempt and then if they make a mistake, we shall definately help them and with pleasure too.

Samarjit Sen
12-04-2008, 06:23 AM
Hi Shabir,

Please download the following link and study the documents.



Any further information required do not hesitate to contact me.

12-04-2008, 02:58 PM

For the accurate calc sheet we need to have more info but if you need very fast one , for your case people using volume divided by 15 for the freezer so you well get the HP for the room you need to cool down and 20 for the chiller . and this factors is good for the small rooms but not for the big project.

Hope it well help you


13-04-2008, 07:17 AM
Back to old style guys do it manually,no software in doing the load calc,hello?no rule of thumb.

Samarjit Sen
13-04-2008, 08:33 AM
I agree that the best way to calculate the heat load is to do it manually. Even if one uses a software, he should have knowledge to use it and to put in the inputs. I remember that some one in this forum very rightly said, that a softwre is as good as the person who is made it.

My sincere advice to the young engineers is that you have to make your basics strong and to help you in the same there is no other source better than this forum. A lot of studies are required and there is no shortcuts.

13-04-2008, 08:47 AM
Back to old style guys do it manually,no software in doing the load calc,hello?no rule of thumb.

I agree with not using rule of thumb.
I am sure that with good software who have all needed inputs and calculations we could much faster and accurately make calculations then manually.
I don't see reason why not use software, except not knowing how to use it. It is tool and results are of such quality as quality and quantity of data have been inputted in to him. Like hammer and piece of sheet metal. The product is good as skill of craftsmen who hits that hammer, quality of hammer and quality of sheet metal.

21-04-2008, 03:49 AM
For serious calculation you can use the web :
heatcraftrpd , and

For estimate : Use the attach Quick calculations from Heatcraft.

I attach also a very simple and accurate little software.

Good luck

24-04-2008, 03:59 PM
but one must be kind enough to give the formula and all the neccessary detail for consideration so that others can start working from there, remember not all have access to mordern technological developments some have and RE is their only help

B G Scott
01-05-2008, 12:44 PM
One of the best FREE software programs is CoolPack its in English or Danish and is comprehensive for all types of heat load calculations.
Do a internet search you will get to it and the down load does not take very long.

B G Scott
01-05-2008, 12:45 PM
One of the best FREE software programs is CoolPack its in English or Danish and is comprehensive for all types of heat load calculations.
Do a internet search you will get to it and the down load does not take very long.

Rember some one who never makes a mistake never knows a mistake when they make it

08-08-2008, 07:46 PM
Dear all,

Please provide easy heat load calculation format in excel sheet.

Manish Jha

08-08-2008, 07:47 PM
please provide easy heat load calculation format in excel sheet.

Manish Jha

08-08-2008, 10:11 PM
please provide easy heat load calculation format in excel sheet.

Manish Jha

Did you ever read rest of posts in this thread? Did you tried search function of this site! :eek:
Do you also want cookie!:D

25-03-2009, 11:29 AM
please reply me how to caculate heat load