how do economizers work

[blueridge2]

Water side economizers have been around for over 25 years from most all CRAC manufactures. Within the last 2 to 3 years the big three are offering air side economizers for their units.

These make more sense for a Server room than for a office building. The IT geeks need to learn that colder is not always better. Check ASHREA TC 9.9 for more inforation on Data Center design.

[VTP99]

[QUOTE=matt1124;13612181]

lol either the ac is pulling down past the ambient temp OR the burners kick on for heat. This year there was only a handful of days they'd "open and save $$$$$$" and I'm sure summer to winter will be the same story

What part of the country are we talking here ?

[VTP99]

The economizer module also handles the min OA position for ventilation needs during occupancy. If your OA and relief dampers aren't at least slightly open when your space is occupied, you likely have a code violation. Turning off minmum fresh air when occupants are around is not an acceptable strategy except say when your furnace fails completely and you need to freeze protect the building.

Is it not 10% min. for the national code ?

[19characterusername]

It's in all IMC based codes and just about everything else. When a space is occupied you have to ventilate it mechanically or naturally (5% of floor area in operable window free area and nothing more than 25' or so from an operable window). The inspector isn't a commissioning agent, so he's not going to do enough checking usually, but that doesn't mean it's not a requirement. I always try to check OA dampers on punch lists, but that's no match for a jumper wire and a client who's been told that engineers are nit pickers.

[19characterusername]

Min OA depends on occupancy. IMC2009 and ASHRAE 62 are 0.06 CFM per sq ft plus 5 CFM per occupant for most occupancies. Gyms, classrooms and other spaces with higher activity rates or space rather than occupant source contaminants will use higher rates. Older codes are 15 or 20 CFM per person. Depending on the load that may correspond to 30 or 40% or even 70-100% using radiant cooling or active chilled beams. On VAV systems you may only need 15% at design, but on part load day you might need closer to 50%. Code effectively requires airflow stations on the OA hoods of VAV air handlers or something else to maintain a OA CFM set point.

[timebuilder]

It's in all IMC based codes and just about everything else. When a space is occupied you have to ventilate it mechanically or naturally (5% of floor area in operable window free area and nothing more than 25' or so from an operable window). The inspector isn't a commissioning agent, so he's not going to do enough checking usually, but that doesn't mean it's not a requirement. I always try to check OA dampers on punch lists, but that's no match for a jumper wire and a client who's been told that engineers are nit pickers.

You must be addressing NEW occupancies, perhaps in office buildings, yes?

In retail, there are literally MILLIONS of retail spaces that have NO outside air at all, and no one is coming to cite them, I can assure you of that.

[19characterusername]

Retail, office, residential, everything. It has to meet natural ventilation requirements or be provided with mechanical ventilation. Even when you satisfy natural vent requirements, there's no ventilation when the windows are closed, so you still want a properly operating mechanical ventilation system.Again this gets picked up during plan examination not by building inspectors, but it could. Street front retail obviously gets some air changes due to people entering and egressing, but NYC for example an IMC 2003 based jurisdiction requires .3 cfm per sq ft of ground floor and cellar retail. Feel free to, with impunity, disregard codes that are not being enforced by inspectors, but you are still in violation and the facility could be handed a violation. More importantly there is a decent amount of research behind ventilation rates. You aren't likely to kill anyone, but you could end up with a smelly facility, tired workers and shoppers, high indoor VOC levels.