VAV Box Retrofit for Ashrae 62.1 Compliance?

[tectonic123]

Hi All-
Noob here and I'm not an engineer, but I need to know if what my building engineer is telling me is right. I've got two old commercial office buildings with new (2006) air handlers and old VAV boxes and thermostats. Per my building engineer, the VAV boxes default closed and only open up when the thermostats direct them to send chilled air into occupied spaces. We want to put in an ASHRAE 62 compliant ventilation solution. My building engineer says the only fix is to put in new VAV boxes, which is going to be quite expensive. My question is, is there any other way to go about this that's cheaper (ie fixing the current VAV boxes open or putting in new thermostats) and is it worth paying a mechanical engineering firm to come in and propose a lower cost retrofit?

Thanks much in advance for any insight you can offer. I looked around for answers to this question but couldn't find anything in the past on it.

 

[tys90]

Well, how is the building heated? You will need to add reheat to the VAV boxes so you don't subcool the rooms when the box goes to ventilation minimum.

You probably want to speak with your controls rep. as well to find out what you are capable of with your existing controls.

The VAV boxes themselves are relatively cheap, it's the things you probably can't do without that will cost (changing controls, adding reheat).

 

[ChasBean1]

"The VAV boxes ... open up when the thermostats direct them to send chilled air into occupied spaces." is correct for typical VAV control - would have to evaluate performance of the existing VAVs to determine if replacement would be required.

 

[Loumolito]

All VAV boxes should have a minimum position to deliver code minimum ventilation air. Th ebuilding engineer is correct. All boxes need to be replaced. The retrofit solution of adding coils will be cost prohibitive.

 

[mauricestoker]

I'd suggest first looking at the test and balance report (TAB) for the 2006 AHU's to make sure that you have sufficient capacity, and that you are getting sufficient outside air. As the boxes only open when the room is occupied, is this on a schedule, or do you have occupancy sensors? If the area is not occupied, look at ASHRAE 62.1-2007 and verify how much air supply you need. If no one is in the building, do you need to do anything besides have a morning cool down period before occupants arrive (no heating is mentioned)? Has there been any problem with humidity (walls sweating, possible mold issues)? A lot would depend on what the weather is where you are at. If lookiing at 62.1-2007, I'd recommend also looking at 90.1-2007. If you have to spend money, look for where you might save money. Depending on where you are located, there may be State or utilities energy assistance programs available.

I'd also recomend looking at the O&M literature to see if minimum box damper position can be reset.

I'd recomend asking your building engineer what controls the VFD.

 

[MechGuy22]

Does anyone by any chance have a excel spreadsheet for calculating the minimum airflow to deliver the minimum amount of fresh air in a VAV system?

 

[MechGuy22]

Specifically im talking about the equation

y=x(1+X-Z)

 

[mauricestoker]

One size fits all might not work.

 

[walz]

Ya i just had finshed a poject, where i needed to have an excel spreadsheet to determine by a logical statement the minimum reheat of VAV....

It was in accrordance with Ashrae 90.1

 

[toughguy1]

Assuming the boxes can't be fitted with heater coils, the engineer is correct. I would at least investigate electric duct heaters. Also, you should be able to set a minimum valve position in your VAV box. Be advised that fresh air adds a lot of capacity to your units, and I agree that you need to get an engineer to verify you have enough capacity. You also need engineering to calculate the multiple spaces equation that Npstewart mentioned. The controls people should control the fresh air damper at the AHU based on the critical space.