Many people today claim to be designing "Green" buildings; however, I think there is a lot of greenwashing going on. What makes a building "Green"? How can I tell a sustainable building when I see it?

-- Christopher Schaffner (chris@greenengineer.com), October 16, 1999

Answers

John:

Thanks for the response.

I'm intrigued by a couple of your comments:

First, you mention primary-secondary pumping systems as energy wasters. Could you explain a bit further? I know that today, many chiller manufacturers are promoting variable primary pumping, but I've always considered primary-secondary to be much preferred to the constant volume pumping schemes many engineers still use.

Second, you finger fan-powered boxes. For series boxes, I will agree with you, but energy studies I've done show that in many cases parallel FP boxes are much preferred to the standard VAV reheat system, especially if their use is primarily limited to early morning warm-up.

Any thoughts?

Chris Schaffner

-- chris schaffner (chris@greenengineer.com), May 11, 2000.

Just by looking at it I can't think of any easy way to tell, anything can be done poorly. For example, an office building with an underfloor system is no more efficient, maybe less efficient, than a conventional duct system if it is designed to have the same pressure drop and delivery temperature (it has happened). If given a chance to poke about a bit, I'd look for the pressure drop accross the fans -- the fans run thousands of hours a year, an extra inch of pressure drop really adds up. Associated to that, what is the face velocity of the air handler? If the ducting pressure drop is .1"/100' and the coil face velocity is 500fpm, IMHO the building was not optimized for low energy consumption. Other common energy clunkers that catch my eye are primary-secondary systems, high condenser water set points to the chiller(s), any Griswold/flow setter valves, undersized cooling towers, fan powered mixing boxes (although there are a few excuses for their existence I suppose) and electric steam humidification.

-- John Weale (jweale@eskimo.com), May 10, 2000.

I will have to think a bit more on the issue of fan powered mixing boxes. I have trouble believing numerous small, inherently inefficient fan/motor combinations can really end up being efficient, but warm up requirements could do it. Basically, you're just using it as numerous small fan coils in that regime. If the fan is used only for warm up... maybe. I generally deal with cleanrooms type facilities -- with only one shut down every year or two, warm up is not much of an issue!

As for the secondary/primary system comment, the implementation I usually see involves three way valves bypassing at the coils for control. Often there are no variable speed drives on the secondary pumps. Sometimes the secondary loop has double the flow of the primary loop (think about that one for a second). Even assuming it is designed correctly and not 'fixed' badly (need more flow... lets double the secondary pumps!), only a pump rep could honestly appreciate this system.

I much prefer primary only pumping. On the evaporator side, get the minimum flow required for the chiller. Put in /one/ set of pumps (slightly bigger, more efficient, cheaper overall pumps) with VFD's. Throw in a controlled bypass right next to the chiller after the pumps (we like flow meters for the extra monitoring and diagnostic benifits, but a delta P one could work as well) and shut off all the bypasses at the coil (or use cheaper, 2 way valves for control if it's new). Control the bypass to maintain the minimum chiller flow. Ends up being cheaper to install and more efficient. When retrofitting a primary-secondary system it's not unusal to end up simply throwing away the primary pumps and running the system on the secondarys alone at a lower speed (the bypasses out at the coils and constant primary loop pumping is a real energy killer).

-- John Weale (jweale@eskimo.com), May 23, 2000.

If you really want to save energy. Use geothermal heat pumps with a closed loop vertical heat exchanger and load matched pumping....

-- Greg Tinkler (gtinkler@enlinkgeo.com), November 08, 2001.