HVAC building pressure differential 1

[Bran8]

Question:
Is there a limit to how much negative pressure can be in a building? Is there an Ashrae standard for this? I can't seem to find anything on this.

Background:
This is boiler plant that is for district heating of a few building around the plant. The combustion air for the boilers is taken from inside the boiler plant building which causes a negative pressure so the operators open a few of the large roll up door to get adequate air flow for the boilers. Opening the doors also causes a noise problem for the surrounding buildings. I have been asked to design a acoustic louver system to provide enough air flow into the boiler plant building. I want to know the negative pressure limit that I should use for the building to ultimately to get a pressure drop criteria for the air flow through the louvers into the building.

Thank you in advance!

 

[Drazen]

Generally, most of building spaces shouldn't have negative pressure as it draws uncontrolled unconditioned air from surrounding.

Moreover, what you describe wouldn't be allowed in areas of legislation where I work. It is only small boilers with atmospheric burners that are allowed to take air from interior spaces. In all other circumstances boilers must have direct combustion air path from the outside.

 

[Bran8]

I don't think it is allowed under legislation any more. The plant is just 60+ years old and those boilers were installed in the 50's/60's when this design was allowed. The new boiler we are installing will have a direct combustion path from outside. However, the legislation considers these old boilers as grandfathered and do not have to be modified to meet today's code/standards.

I am going do what I can to minimize the negative pressure in the building. I am just looking for a guideline or some sort of requirement that I should meet; i.e. a max negative pressure requirement in a code or the force required to open a door due to pressure differential.

 

[lukaiENG]

I think it will come down to how much negative static pressure your boilers can handle. If you choke of the air they will have incomplete combustion and this will cause you issues with soot and pollution. You're probably better to put in a fan assist system to get the air into the building, but this will be costly of course.

 

[dbill74]

First question, where in the world is this boiler room located?

As for an ASHRAE standard, I'm not sure and a quick look isn't finding one. However, there is the International Fuel Gas Code and NFPA 54 National Fual Gas Code. If in USA, select states have edited IFGC to create their own version. All of which provide direction on quantities of combustion air per BTU. From there you can size your louvers.

Regarding your question about the building being negative. Don't do it! Areas or spaces within a building (i.e. the boiler room) may be negative relative to adjacent spaces within the building, but your building overall (including boiler rooms) needs to remain positive.

Keep in mind that the air in most spaces can transfer through other spaces (although air from select spaces such as toilets can't), but no code is keeping you from using air that would otherwise be dumped to the outisde from going to the boiler room as combustion air. Practically speaking it may not work, but that is something you have to workout.

 

[BronYrAur]

Are we mincing terms here? Isn't any boiler room that has only louvers for combustion air considered negative? The "negative" we want to avoid here is to starve the boilers of combustion air, but the room will always be negative when the boilers are firing, which is what draws in air through the louvers.

As dbill74 says, size the louvers per the Fuel Gas Code and you should be fine. Something tells however that the required size will be too large to install (due to lack of wall space, etc.) In that case, a large makeup air unit is probably in order.

 

[GT-EGR]

As far as combustion air intake sizing is concerned, your goal should be to meet the fuel gas code requirements, either through direct openings to outside, or the fan assisted method. Keep in mind that negative pressure boiler rooms really shouldn’t have refrigerants that could potentially be swept into the combustion process in the event of a leak. Just because an installation is grandfathered in, doesn’t mean the intial target shouldn’t be to modernize to today’s standards.

When it comes to allowable nagative pressures in general, somewhere in the building code there is reference to no more than 5 pound force to open a door. So for arguments sake if someone want to put details on your intake goals, you apply a pressure to the door, based on its size, knob location, crack openings, etc - that leads to create no more than 5 lbs of force to overcome the pressure to open the door.

This would then become your target pressure drop over your new openings - which includes the louver, damper, attenuators, screen, and anything else in that intake assembly.

 

[joecampbell]

what your saying didnt meet code in 1950 either.