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[EnergyPlus_Support] Re: DOAS is good... is bad
Thanks for your insights, Dr. Li. Yes, you are right, Dr. Li. The ODA required for split systems is really minimal. In Germany only a few spaces are reqired to have more air than needed for people (like showers and toilets. I find that previous trends of using say 2.5 Air Change Rate for fresh air requirements has fallen to sometimes below 1 (where previously even storage space was given at least 2 ACH). This is driven by new norms that try to encourage energy savings (EnEV 2009). The architects are under more pressure and our typical installation space height for a office corridor is about 1.2 m... and getting less. As we are usually required to have smoke exhaust (spaces larger than 20m2) of 10ACH together with sprinkler systems, it gets tight with installation. The chilled ceiling panels are hinged for access. They are a lovely luxury, but often a practical solution. Large industrial factories are known to use them due to the increased comfort factor that radiation gives, which then allows less heating or cooling to be implemented.
I've recently finished an interisting project, a 6 story office, where the radiant ceiling was a mesh of easily bendable and shapeable net of tiny PVC pipes which are "painted" directly onto the raw ceiling slab of the office space (giving loads of height).
Unfortuanately, this minimal air trend is causing moisture problems in summer as their is an increased risk of stagnant corners where the air does not move.
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, YuanLu Li <yli006@...> wrote:
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> I have read the Wikipedia article on DOAS. I am not convinced that the sensible and latent heat load can be separated and more efficiently served using two parallel systems. I am not against the use of DOAS. In most HVAC application, I do not see the need of it, if you are already using an air system. If you use baseboard heater, water radiator there may be a need to feed in some fresh air. The volume of air involved is relatively small, and is generally proportional to the number of occupants. No body would bother with DOAS, if there are only two or three occupants in a multi-room house or flat. In a high rise condo, the DOAS is used to feed the corridors and the common area. There is no other way to do it, because the air is forced to leak into all the apartments, and there is no return duct. The fan is mounted at the top of the building, blowing OA with slight heating or cooling, down some vertical shafts, with a diffuser at each floor. Individual apartment will have its own fan coil unit with its own thermostat control. In the apartment using baseboard heating in Winter, the corridor air is exhausted through the bathrooms ceiling vents down a common shaft to an exhaust fan in the basement level. The warm air was used to heat the garage area. In Summer, the Windows can be opened. The basement exhaust fan will still be running, but the air may be from the opened windows. The windows in high rise apartments cannot be opened to a width of more than 3 ins. by law in Toronto, Canada. This is to prevent children falling out of a window. However, there are still a few children falling off the balcony. This municipal by-law has definitely increased energy usage, because cooling is not required in Summer. DOAS is just another air system. It is there for convenience rather than separating the sensible and latent heat load.==========================The radiant panel is useful, when the low air noise is a requirement. As a ceiling panel, I would not sit under it. I do not feel safe with all the weight and the water above me. It can be installed vertically in a partition wall, so that it is invisible. It is not cost effective, and have many problems associated with the pipes, insulations, water vapour barrier, etc. Sharing the pipe with a fire safety system is also not a practical idea, as the water flow capacity is limited. The simulation of the radiant panel is quite simple. You simply declare the ceiling with a construction that can install the pipe. The layers are optional and flexible. For night cooling water storage, I was proposing a water tank instead of the pipes. The exposure of convection air to the tank surface is the control for releasing the cooling effect to the room. A porous panel will produce some cooling when some moisture is condensed on it and then allowed it to evapolate by air movement.======================Under floor piping is now offered as a standard rough-in by builders in Toronto for a basement floor which is level with the grade. The room is usually used as a family room > If the chilled beam is on an exterior wall, then more insulation is required on the outside. If the chilled beam is between floors, why should the owner of one floor pay for the free use of the other side of the floor, unless it is common installation such as school or public buildings. If cooling is not required, chilled beam seems to be a redundant system.If it is used for heating, the temperature must also be limited in a real system. For simulation, I do not think there is an expansion limit imposed.===================I am not against the use of any of these systems. I treats them as luxury items and are not really energy efficient in a HVAC system.
> Dr. Li
> To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> From: jeannieboef@...
> Date: Sat, 30 Jul 2011 13:48:55 +0000
> Subject: [EnergyPlus_Support] DOAS is good... is bad
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> Hi all, we started a discussion a while ago on the pros and cons of radiant ceiling systems. I just by chance came across a wikipedia (sorry about the reference) round up on the authors take on DOAS.
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> http://en.wikipedia.org/wiki/Dedicated_outdoor_air_system
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> I've also read some ASHRAE journal on the topic, but I'll have to do some fishing to find the articles again. This topic is actual for me and all others in Europe. I have questions:
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> 1) When modelling chilled ceilings in eplus (not chilled beam induction or forced air units), I currently construct a construction for the ceiling with slab, insulation, Aluminium sheet 1mm, internal source, Aluminium sheet 1mm. As the panals are in reality just pipes strapped to a porous metal sheet that hangs like suspended ceiling, should I still build in a Air gap in my construction above?
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> 2)Is this the best approach? Should I do something to mimic the porosity of the sheet?
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> 3) Most air supply diffusers are designed to "stroke" the ceiling with supply air to maximize the convection transfer. Is it worth modelling with advanced convection coefficients on these surfaces?
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> 4) Unlike a heated floor where the pipes are really asphalted in, these panels represent a separate zone equipment, like a fan coil. I find the current way that I model these very tedious. Is there any word on a future object, like the chilled beams object to make this more user friendly?
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> 5) Would using the chilled beams object be a better, more accurate work around and how would I set it up.
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> ...And last but not least...(especially Dr. Li)...what do you think are the advantages / disadvantages of DOAS?
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