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New Task given - slightly outside my experience level

New Task given - slightly outside my experience level

New Task given - slightly outside my experience level

Hello I am usually a mech installation engineer. I have Done large duct work installation and also helped do calculations before about the support calculations from steel work before. I am primarily a site guy anyway. But I am now in an office and have been given the task to do a preliminary design on some temporary HVAC in an enclosed concrete building which will be used during the construction phase.

To put it simply what I can work out is to size the duct, work out the duct head loss due to the length and then size the fans. What I have no idea what to start on is to calculate approximately how much air need s to be going into the place and extracted. I guess I have to work out the area of the enclosure then work it out from there about how many times the air needs to be replaced.

Anyway What would help if someone told me the steps to starting a prelim design on this would be please (then I will look into it and perhaps ask more specific questions later). What I think I need to calculate is this:

1. Size the enclosure
2. Determine how many times the air needs to be replaced
3. Do a rough lay out design distributing the air in and out based on the plant to be installed
4. Calculate the duct sizes
5. Calculate the head loss
6. Size the fans ( I guess there will be minimum 2 fans in and 2 fans out)

I just need to start somewhere to get a basic idea of where to start and evaluate what I need to learn thanks very much. Obviously I have room for error in this as it will be designed by experts but within a few months we need to have a rough idea of what is to be expected.

RE: New Task given - slightly outside my experience level

Your airflow rates are going to be dependent on the type of space you're looking at.. What is the purpose of the enclosure? If you have access to any ASHRAE resources they can help determine the types of airflow required. Some things that you will want to consider:

1. Is the airflow provided for ventilation purposes only?
2. What type of air handling unit will be moving the air? Is there re-circulation?
3. Does the air provide any heating/cooling to the space?
4. Are there exhaust requirements for the space? (Exhaust/ make-up air system?)

If for example, your enclosure is to be a temporary office space and your purpose is to simply provide enough ventilation air for the occupants, a simple ASHRAE calculation would be as follows:

ASHRAE Standard 62.1:
Occupant density = 5ppl/1000ft2
cfm/person = 5
cfm/sqft = 0.06
Sqft of enclosure = SQFT (do you know how big it is?)


Ventilation rate = (5 ppl/1000ft2*SQFT)*(5cfm/person)+(0.06 cfm/sqft * SQFT)

This will give you the fresh air required to be delivered to the space.

As you can see, details matter, hopefully this helps.

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