HVAC Duct Design for Value Engineering

[Buildtech2]

Recently, I have designed an HVAC system for the workshop where maintenance and repairs of machine components will be carried out. The air conditioning to the workshop was provided by 4 nos. DX package units and these units were placed outside the perimeter of the workshop. Form each package unit, the supply and return duct work was penetrated into the external wall and run internally adjacent to the wall at 3.5 meters from finish floor level with side wall supply wall grilles and registers.The following points justifies the internal duct work proposal as compare to the external duct work around the workshop perimeter. According to internal duct work proposal, the internal duct work was already installed on the site. Now the client need justification of proposing the internal duct work as he thinks that external duct work would have been a better proposal in terms of value engineering. I expalin him the following points for considering internal duct work but he need more explaination.

Can anybody provide me a better explanation of internal and external duct work in terms of value engineering specific to my case. Please note that the proposed workshop is located in the Arabian desert where peak external temperature reaches to 120 F and in the evening, the relative humidity level sometimes reaches to the saturation level.


Advantages of Internal duct work.

Architectural external appearance
Overall reduced length of ducting work.
The external insulation and duct work are subjected to the high ambient temperature and humidity that minimizes the life of insulation and may add up replacement cost as compared to the internal duct work. This will also cause an ongoing maintenance problem. This problem would be mitigated by routing the ductwork indoors instead.
For external ductwork, thicker insulation with higher density would have to be provided for external duct work (50 mm) as compared to if the duct work was internal (25 mm).
By routing the ductwork indoors, this would also translate into a money saving over the lifespan of the building, due to reduced maintenance costs and considerations.[/li]
For external duct work, considerably more wall penetrations would also have to be provided on the external walls (and potential waterproofing problems) can be avoided by internal duct work.


Disadvantages

Slightly reduced work space.

 

[EnergyProfessional]

Not sure if you understand value engineering. It does NOT mean to make it chaeper by redcing quality. It means giving you the same value at less cost.

With this said, the outdoor duct gives you less value for all the reasons you listed. Exterior insulation will deteriorate quickly, it will lose/gain more heat than interior duct, and willb e more expensive to build.

If you can make space inside, install inside. Maybe you can reduce duct size since it seems the run will be shorter. You also don't need interior liner or insulation, that may help.

disclaimer, I 'm a bog opponent to anything isntalled outside that doesn't absolutely has to be outside. Maintenance is a hassle. Outside it is either cold, snowing, hot, raining, windy or something else i do't wnat maitnenace guys endure. Keep in mind, ultimately all design is for the benefit of people.

 

[SAK9]

I would suggest you calculate heat gained by cold air in both cases and include in your report.You may as well quantify the annual energy saving cost.This won't take long if you have the original heat load files(just tweak the duct heat gain). If the client is still not convinced let him pay for dismantling and installing the duct work externally with added insulation,metal cladding etc.

 

[Buildtech2]

Thanks for providing valuable comments.

 

[dynamo78]

Buildtech, its a go for the internal duct work,assuming that its an open area since ita maintenance bldg, you are not utilizing more area,its 3.5 m affl, and probably the width will be much thinner that the height. should know, I did one for Ghazlan PP in KSA.

 

[willard3]

Value engineering does mean to make it less expensive by reducing quaslity. I have fixed many, many, many systems that have been value engineered and won't work as they were designed.

Value engineering is another term that means the opposite of what it says because it has been overused/misused.

 

[EnergyProfessional]

willard3: I hate to disagree, but value engineering means to provide the same "value" at less cost. It does not mean deleting parts or lowering quality (which would be lowering value).

Unfortunately many designers don't know this andjust cut ost (along with quality).

 

[SAK9]

Value engineering is mostly effective when the client undertakes it.They only can say what bells and whistles will deliver in the long run.
Just to give an example a consultant was proposing CO2 based outside air control for a lecture theater in a uni.Butthe uni engineering services came back it was not required because the lecture theatre was above 80% occupied most of the time.

 

[dynamo78]

Value engineering is helpful if you can quantitfy the function against cost. The principle is as simple as that, the challenge is how to quantify the function Bros.

 

[willard3]

Now imagine the general contractor in isolation with the owner "value engineering" the HVAC system.

Now imagine the Architect in isolation with the general contractor and owner "value engineering" the HVAC system.

This happens all the time which is why it rarely works.

 

[NegativeZero]

^^^^that's called contractor design build....flip a coin and hope for the best.