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Energy Efficiency, ACH, Rooftops, ‘n’ heat recovery

GMcD Member Posts: 477
I have designed those kind of systems, and have some working very well here in the relatively mild Pacific NW. Heat recovery in your climate zone would be an even quicker "no-brainer" given where heating energy costs are going. DV systems are fairly easy to design, but you have to be very careful, and may need to do some CFD modeling to insure that the design is OK for some spaces. A good place to start is EH Price's website for some tutorials. They have a Test Lab at the Winnipeg factory (not that far from Ohio) for hands on testing and viewing. Weblink:
http://www.price-hvac.com/ and go to the left hand side of the page and click on the Displacement Ventilation section (J) - there is a good design guide there including some calculations and "how-to" info.

I am using mainly heat-pipe coils using 100% outdoor air/100% exhaust air in side x side AHU configurations and these work great for passive, simple operation (no tilt crap on my jobs). Plate type HEX sections are also another good passive choice. I like DesChamps and Venmar as the go-to suppliers for the larger units (5000-20,000 CFM). Weblinks: http://www.deschamps.com/ and http://www.venmarces.com/home.php?body=unitary&menu1=1&menu2=1

The key with DV cooling is that the leaving air temp from the AHU must be in the range of 63F to 68F which is higher than standard/conventional AC systems that like to push out 55F air. You may want to check for whether you need de-humidification in the summer with the elevated supply air temps, the cooling coils may not de-humidify enough at the desired DV SAT. So, no problem- use a small refrigerant DX cooling coil to dehumidify, and face and bypass mix off the heat recovery section for the reheat back to your desired SAT.

This is a real abbreviated crash course, and I suggest you start reading and doing some weekend google searches on "displacement ventilation" for a ton more technical data. Halton (English firm) has a good website with DV products and a software package for design of DV systems but you need to acquire that package through a supplier.


  • ttekushan_2
    ttekushan_2 Member Posts: 57
    Energy Efficiency, ACH, Rooftops, ‘n’ heat recovery

    I’d like to hear your opinions on some issues I’ve been thinking about.

    But first: I’d spent the better part of this past winter working at an old industrial building that's converting to a retail/mall/ restaurants/market. Great building with the 16” thick reinforced concrete floors, 20’ ceilings, huge windows (but new with insulated glass), about 100,000 square feet in all. Two floors. I know the people quite well and was called in to give the the straight story on their “little” steam heating system and its troubles. The usual troubles. Traps bad (LOTS of traps), piping miscues during varied repairs, and areas that need various attention. Nothing terrible, but quite a bit of $ because of the size of the system. The fun part was adding the big projection heaters to the north side part of the system (don’t worry. Plenty of boiler for it). Added Tekmar 269 control. Everything’s fallen into place. Heck, the net flue temp on the boiler (150 HP!) is 340 F and I haven’t cleaned or adjusted it yet! Its been well maintained, you see.

    So I am informed by “part” of future management that the system may not even be used. Specifically, the restaurants necessitate make up air, and since "everyone" uses rooftop units now, they are going to install rooftop units for ventilation and A/C everywhere. Since they include heat, its obvious by the AFUE numbers that these are the best and most efficient way to heat the space in winter. When I suggested the existing system could very likely heat the load more effectively and economically in a structure as this (with the addition of a couple of steam coils for make-up air), they dismissed the idea out of hand. Satisfied that the proposed rooftop configuration could not effectively heat so many of the “non make up air” spaces around the building, I figure they’ll find themselves using old steamy anyway.

    But seeds of doubt planted early on are bearing some kind of fruit (seedlings? Darn metaphors). So called efficiency is now the mantra of the ones dismissing the steam system. So I asked about the complete lack of roof insulation. Surely 55,000 square feet of uninsulated roof should concern them? Air conditioning load; Have you thought about displacement cooling (blank stare)? How are you recovering heat from your winter exhaust air (“uhhhh”)? Now they’re starting to ask questions, but I don’t have enough specific answers.

    I want to be able to competently direct them to products or vendors that deal with some of these things. Specifically displacement cooling in summer and exhaust air heat recovery in winter. But I seem to feel more lost in this field the more research I do.

    Is displacement cooling presently made up of the standard cooling components that are built into a custom arrangement engineered and then installed by a HVAC contractor who knows this stuff? Or are there now units prefabbed like the roof tops or make-up air units that can do this duty? Or is this the domain of “green” building consultants because the idea isn’t mainstream enough at this time?

    The same questions hold for exhaust heat recovery in the winter. Are air-to-air heat exchangers the prevailing way this is done? Is it done much at all, or do regional preferences and codes prevail?

    I’m in northeast Ohio, where wintertime efficiencies attract the most attention but creative solutions take a long time to catch on. And cooling ain’t getting any cheaper either. I’m the steam guy, but I think its time to look into a more integrated approach to energy management.

    Any thoughts are welcome. All I really need is to be pointed in a solid direction. Still wandering.

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