HVAC Design

[JG MechEng]

Hi everyone,

I have been asked to design an HVAC system for an electrical substation. I am a mechanical engineer but my experience is in process equipment design so I am way out of my area of experience. I know that ASHRAE is the design code for HVAC systems, but I'm not sure specifically which parts of the standard I'll need. This is an electrical substation in a chemical plant. There are no windows, two doors and a pitched roof. The area is not a classified area (no explosion proofing is required and I dont need to run a purge or positive pressure in the building). If someone could point me to some literature that I could reference and the specific ASHRAE handbooks I should get it would be greatly appreciated. Also any considerations that I should watch out for such as managing the humidity and staying away from the due point would also be greatly appreciated.

regards,

JG

 

[Compositepro]

I'm not aware of any standards, except the desire to protect your investment. The atmosphere in most chemical plants is somewhat more corrosive than average. Supplying clean filtered air at a positive pressure will keep your electrical equipment alive longer.

 

[lilliput1]

Find out from the electrical equipment manufacturers their corresponding temperature and humidity limits. From this determine which equipment require air conditioning and which can just be ventilated with the outdoor air maximum temperature and humidity level.

 

[LittleInch]

Why are you trying to design it?

Just pull together a data sheet and get HVAC vendors to do the design. Max temp inside and out, heat load, sun load & humidity levels.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[willard3]

Letting vendors do your HVAC design is unethical and you will still be responsible for the result.

 

[lukaiENG]

You need to determine the heat lost from the electrical equipment. if it is a substation it will have transformers and switchgear.
Electrical equipment manufacturers can provide you with heat losses due to transformation and distribution within their equipment.
[ul]
[li]Depending on type/size, a transformer could have losses from 0.5 - 3% of the transmitted load.[/li]
[li]A 480V 4000A switchgear panel could have a 10-20kW load depending on the number of sections or breakers. It adds up pretty quickly.[/li]
[li]High voltage switchgear has lower heat losses but should also be evaluated.[/li]
[/ul]
Depending on your maximum ambient condition you may be able to get away with ventilation, but in many locations you may need to provide cooling.
If you're lucky, the transformers are outside, this removes a sizable chunk of the load from the building.

 

[JG MechEng]

@Willard - I dont fully agree that its unethical. outlining the design parameters and letting a vendor design the system is common in the petrochem industry and is often preferred. Liability is only with the sealing engineer and i wouldnt be sealing it if the vendor does the design...BUUUT...I have spoke with vendors in the area and they all expect the engineering firm to design the system and tell them what to provide and where to put it.

@LittleInch - See my above comment, i tried this approach and the vendors didn't want the responsibility...although i was searching around on the TRANE site and they have what appears to be very robust software. I have a question into the support group if they offer design services. I am hoping I can get a design build package from them.

@lukai & lilliput - Thanks for the info, Im making a sheet of design considerations and ill be adding your info to that. It will be used if i design the system, or just have to review a vendors design. Thanks again! also...transformers are outside, only switch gears and buckets inside.



All this info is very useful, but my original questions hasn't been answered yet. I design process equipment and we use ASME Sec VIII, ASCE 7-10, ACI 318, and various other design standards / codes. Which design standards are used for HVAC...ASHRAE? and what sections of those standards should I look into?

 

[MintJulep]

There is no ASHRAE standard for "Electrical Substations in Chemical Plants".

In fact, except for a few specific cases, ASHRAE standards do not work the way you seem to hope that they do.

"I have been asked to design an HVAC system for an electrical substation. I am a mechanical engineer but my experience is in process equipment design so I am way out of my area of experience."

You might consider replying "No thanks, that is not my area of experience."

If it's too late for that then consider sub-contracting to an appropriately experienced engineer.

This job will probably not be as easy as entering a few parameters and selecting the equipment that the Trane software tells you to select.

Anyway, ASHRAE Handbook Applications Volume Chapter 27 and maybe chapter 31 would be a start.

 

[JG MechEng]

@MintJulep - There are some special circumstances to why I'm taking on the project, but if I were following normal working procedures...I agree with you...stay in my area. But that's not where I'm at so I'm reaching for help! I also know that there is not a standard for "Electrical Substation HVAC in Chemical Plants" just like there isn't a standard for "Pressure Vessels in Chemical Plants". But we do use design standards and I'm sure that there are some that can be applied in this situation and I'm asking those in the know about HVAC to point me in the right direction. I'll take a look at ASHRAE Handbook Applications Volume Chapter 27 and maybe chapter 31.

If an HVAC engineer would ask me about pressure vessel design I would point them towards Compress Pressure Vessel software, Pressure Vessel Design Manual by Dennis Moss, and ASME Section VIII, Div. 1 (and recommend they stay away from Div. 2). So I'm asking the HVAC community for similar guidance, specifically like @lukai & lilliput provided above.

 

[GerardNavarrete]

Are you still looking to build the HVAC system? Well, this is a great initiative to start with. As we all know that HVAC is the complete package of home appliances that can be used a various place like in offices, homes, etc. for ventilation, air conditioning or heating purpose. While designing such a system in an electrical place you need to keep several factors in your mind regarding your safety. A complete HVAC system consists of several small devices like air cleaner, condenser, chiller, heat pump, etc. I am still in confusion how will go to configure these devices in that place? Every device has its own significance to run complete HVAC system. You can click over here to have detailed information about the HVAC system.

 

[chicopee]

lukaiENG provides the correct method but also consider sun exposure, ambient temperatures and humidity as mentioned in other posts, and air infiltration.

 

[LittleInch]

JG,

I know what you mean, but I'm not sure ASHRAE do the same as you know that ASME does for piping and vessels tc.

The best thing is probably to join as an associate member for $209 and get one year access on line to their four volumes of the handbook.

what sort of load are we talking here?
If it's just a switchroom with no big heat sources (VFDs and the like) then you can probably simply use some ( 1,2 or 3) large duty three phase packaged units with a ceiling AHU and an external skid.That's all that a recent packaged vendor for a switchroom did for me.

If you use a decent vendor like Mitsubishi, carrier, LG, Daikin you'll be good and then just hire someone to fit it and commission it. Look then up, talk to a loval rep and away you go.

Condensation on the equipment only happens if you cool the place down and then open the doors on a hot humid day.

.


Remember - More details = better answers
Also: If you get a response it's polite to respond to it.