It seems a lot of attention is being made of tight control systems relating to rooftop units. There are slick devices available that can help you control the discharge air conditions. Before you commit the client’s money to that technology, consider the net result to the system.
Hint: Consider how you control a shower and a bath when you answer.
Are you mixing (bathtub), or is the air going directly on the occupant (shower)?
Most applications are mixing, and if you are indeed mixing, the requirement for tight discharge air controls may not be critical.
When you give your kids a bath, and the water in the tub is cold, you don’t turn the water to some intermediate temperature. You move your kids out of the water and you turn it all the way up. That’s pretty different when you give your kid a shower, isn’t it?
Isn’t the bathtub like mixing ventilation and the shower like displacement ventilation?
There’s a lot of neat specialty equipment out there. Digital scroll compressors. Modulating supply gas valves. Modulating hot gas reheat. The value of those systems won’t be taken advantage of unless the air is going directly onto the occupant, such as in displacement ventilation systems.
When you specify or consider designs that offer these neat features, (and they are neat), consider the application before you begin. If the system is mixed, the sophistication requirement drops significantly for the discharge air control.
If the application is DOAS, can the room equipment handle some variation in the supply air conditions? It probably can.
If comfort is the issue, getting better mixing out of the diffusers may improve the performance. Consider high induction diffusers from Price such as the SMX or the RVD. The higher induction may make any potential comfort issues go away.
If you have engineering questions related to this or other Air Flow products, contact Tom Gelin at tom@airflowinc.biz or 414-351-7744.
