Hi everyone, recently I'm designing an air cooler with four different services.
Becuase three aircoolers were very smal with low duty,client wanted me to merge all aircooler services in one unit.

So i designed all of those four aircooler services in one unit with four bundles each of them for each of services.

Now I have three question:

1- It is possible to design multiple services in one unit, you could determine face velocity one time for all services, but when you run the software, it calculates different face velocities for different services, I couldn't understand concept of this, i use one common fan and bay for all of them,how it ispossible to each service has a different face velocity?

2- I received one run time message that says fece velocities between servicesvary more than 10 percent.
I couldn't find anything related to this in guidlines and design ractices, anyone can tell me whats the consequence of this problem? I mean what does happen if i design this aircooler unit with four different services and face velocities of them vary more than 10 percent between services???

3- I could design three of services with almost similar overdesign, but for one of services the overdesign is muchmre than others and if I try to limit the overdesign at the same level of others while meet the temperature aproach criteria of project for this service, face velocity of this service increases to the range around 4.5-5 m/s while others are at the range of 3.2-3.5 m/s. So I don't know should I try to keep the face velocity at the same level or overdesign?

Anyone coul help me?

A few miscellaneous comments... You seem to be using some software (?) for design that gives you a message you do not like. Does it matter? Is this one fan bay or multiple? Is there any process consequence if the unit were overdesigned? I would put the overdesign into 'safety factor' category. If you must restrict air flow, consider using louvers or variable speed fans. Maybe dummy tubes could fill in the extra air-ea.

Thanks Pilesar,
Yes I use HTRI software.

Overdesign isn't my problem itself.Actually difference in overdesign of services in one aircooler unit (one bay two fan and four bundles for four sevices) is my problem.

I considered 20 percent overdesign by mysef for safty factor because it is in basic design phase.

But for one of services I reach 50 percend overdesign.

The lovers act for all services in a similar way so I coul control one service with louver independently.

Thanks nikolay

I don't see the concern. What does it matter if one of the bundles has a 50 percent overdesign? It sounds like you did good work combining all four services into one unit. The total unit will still be one bay and two fans. Why care if the overdesign factors are not equal? As long as the unit works acceptably for all four services, how will further optimization save significant capital cost? An analogy: My car is overdesigned since it has a back seat that no one ever rides in. There is no compelling reason for me to remove it so I leave it in the car.

It does not appear that you are designing the units. The usual route is to prepare a spec for design by a vendor.

 

Bobby

It does not appear that you are designing the units. The usual route is to prepare a spec for design by a vendor.

Bobby

Bobby I don't understand what do you mean?!!!

Firstly, currently project is in basic design stage, I don't know your company and country, but in our country, in this stage no vendor has been selected.

After detail design, designed sepec is proposed to vendors and they do their calculations and designs based on what they have and offer back to the client with their recommendations.

Secondly, Why should I bother myself to ask this question to solve the problem?

Thirdly, Does it matter do I design a unit or not and why I ask this question and what is my intention?
Here is an Engineering and scientific community which people discuss about engineering subjects and problems. So what does it matter why I ask this question and challenge?

I don't see the concern. What does it matter if one of the bundles has a 50 percent overdesign? It sounds like you did good work combining all four services into one unit. The total unit will still be one bay and two fans. Why care if the overdesign factors are not equal? As long as the unit works acceptably for all four services, how will further optimization save significant capital cost? An analogy: My car is overdesigned since it has a back seat that no one ever rides in. There is no compelling reason for me to remove it so I leave it in the car.

Pilesar, thanks for participating in discussion.

Overdesign can have its own problems, at the first it affects on economy of project and the engineering is about solving the problem with the lowest cost.

But it can cause problems technically too.
For example from control aspect of the problem. Overdesign can cuase unwanted process problems in downstream, and can cause problems for turn down ratio.

In this case,at first it was my strategy and personal rule and discipline to design all the units with the same overdesign as much as I can do and is possible. I think it is an expected engineering practice.

Secondly my next technically concern is control of process because all four services are integrated into one aircooler unit so usually any change on control of hardware of aircooler affects on all services together.
So I as designer try to design the units so that solve the problems in this stage as much as possible and decide about them by myself and don't leave them to vendor and construction options.

Change your pass arrange, number of tubes, number of rows, fin height etc. Each section will have a different airflow velocity if you have different number of rows, pitch, tube size, etc. If you add rows in a bundle it will force air to another bundle. It’s creating a larger back pressure. I use HTRI also.