Chilled beams - outside air requirements

[remp]

I am designing a passive chilled beam system for an office developement. How much outside air must I deliver. Is it enough to deliver 10L/s/person (normal code requirements even though less can be acceptable). Assuming 1 person/m2 thats 1.0 L/s/m2. Is this enough for air distribution. Do I need more. What supply air diffusers are needed to disrtibute low air flows. What is normal in passive chilled beam installations?

Your advise and help would be much appreciated.

 

[GMcD]

Passive chilled beams - like no air being delivered through them? Then they will only be doing sensible cooling. Basic room loads calculations apply, if you are using overhead mixing air distribution - if the total heat gains in the space are say "100", and the chilled beams can offset "40", then the air side must supply the "60" remaining. Minimum outdoor air = Code requirements. Total airflow must be Code minimum fresh air + air needed for latent and whatever sensible load the chilled beams can't handle at whatever supply air temperature you are choosing for the air supply system.

If you are doing conventional overhead air supply, just use normal ceiling diffusers sized for the airflow required.

 

[atlas06]

The literature you should be reading is the "induction units design" they operate in a similar fashion.
But I sense that you have a difficulty in applying this technology, you may want to get the manufacturers to help you somewhat (and I say somewhat because they will sell you fish in the sea).

I feel your pain my friend, It sucks when people start advocating all these new systems but they become top secret technology when it comes to design help.

Good luck.

 

[ChrisConley]

I'm a big fan of ACB's (active chilled beams) and would offer the one additional though for O/A requirements. Chilled beams (passive or active) can only supply sensible cooling. The latent cooling has to come from your ventilation system.

Most of your internal latent loads come from people (200 Btu/hr per person... depending on activity level) so the code required minimum outdoor air might not be enough air to meet the load.

Also, chilled beams effectiveness is dependant on the chilled water temperature, the lower the better. The chilled temp must be set above room dewpoint, so the lower you can control the room dewpoint the lower the chilled water temp, the more efficient/effective the beams (which reduces capital costs).

Finding a balance can be challenging, I've actually used small dehumid units to try and control latent without paying the outdoor air penalty... but it adds to capital costs.

 

[MarauderX]

Instead of passive chilled beams you may want to look at radiant panels. No ugly mess to sell to the architect, less engineering hassle, and less maintenance issues.

The ventilation requirements remain the same - you can use a dedicated OA system to serve directly to the spaces you need. For a chilled beam system, there are units that you can feed the OA into, but be aware that condensation from unmixed air may be a serious problem.

http://www.eypmcf.com

 

[bbohsali]

Like most other HVAC system, chilled beams will perform in a satisfactory manner if designed, installed an operated properly.

Most (if not all) building codes require that we provide ventilation air into an occupied space. The ventilation air serves multiple purposes including helping keep the concentration of indoor contaminants in check and providing pressurization for the building relative to outdoors.

In the (old) induction unit system, the primary air fulfilled several requirements including: creating the induction air stream as it leaves the nozzle, ventilation air, space pressurization and latent cooling.

Active chilled beams operate in a similar manner, albeit without the need for high pressure on the primary air. For example, primary air supply to induction units typically requires 1-inch w.g. air pressure at the terminal, compare this with ~1/3-inch for active beams.

Passive beams can be used as a supplemental (sensible) cooling device in a space. The space must have a "primary" source of ventilation air to meet code and to offset the space latent load, otherwise the humidity in the space will start to rise and eventually the passive beam will start to show condensation. Therefore, setting the right supply air temp and humidity of the primary air is paramount to the success of the passive beams.

Regards