HVAC Presentation problems

[Antechs]

Hi everyone. I'm a student of HVAC and will be finishing from the program in May. This semester I took a commercial HVAC course, because I have only learned about residential systems in prior semesters. First week of class the professor drops a presentational project on us which is due next week for our group. Our focus is CAV systems. I have been trying to gather information on CAV's but haven't found any great sources, and the info I have gathered isn't helping me understand my topic. But from what I understand CAV systems are used for large open rooms, I think? I have found some contradictory info to that understanding.
I was hoping someone on here could help me get a good understanding to what a CAV system is? What circumstances are they used for? Pros and Cons? And what exactly is an air handler? Someone told me that a furnace is an air handler, it makes sense, but I've never heard a furnace called that. Are there any websites or good books to help orientate me with CAVs? Thanks.

[amd]

was hoping someone on here could help me get a good understanding to what a CAV system is?

An air handling system which delivers a constant air flow rate each zone regardless of the cooling/heating demand.

Most newer systems are variable air volume type, meaning that the amount of air delivered to the room varies to meet the cooling demand.

Typically an air handling unit supplies air at around 55F; under normal circumstances, the air handler mixes indoor and outdoor air supply air to maintain the (supply air) setpoint. If the supply air temp is too low in the winter, the supply and exhaust air dampers close (mixed air damper opens) until they reach minimum position (a certain air exchange rate is required maintain good IAQ) or the setpoint is reached.

If the setpoint can not be reached in spite of providing minimal ventilation, the heating supply water valve opens.

In warm weather (outdoor air above 55F), the supply/exhaust dampers close until they reach minimum position and chilled water (provided by a chiller - an air conditioning unit which cools water instead of air directly) is used to maintain the supply air setpoint.

Constant air volume type systems, as the name implies, don't vary the amount of air going to each zone; instead, reheat coils are used in each CAV box* to maintain the setpoint. (Some older CAV systems are "dual duct" - each zone box mixes hot and cold supply air to maintain a comfortable room temperature; these systems are horribly inefficient - the engineer who came up with the idea deserves to be shot. :p )

(*Commercial HVAC systems are zoned. Each zone has a box with a damper maintain desired airflow and supply air temperature)

Variable air volume type systems, on the other hand, vary the amount of air going to each zone provide the correct amount of cooling to each room. When the setpoint can not be maintained (supply air damper at minimum position), the supply air is reheated to maintain the setpoint.

The disadvantage of CAV systems is that the waste an enormous amount of energy reheating air which was previously cooled (either by mixing return air with fresh air or using chilled water) to maintain a comfortable indoor temperature. Hence, they aren't used much in new buildings, as energy isn't cheap any more..

The advantage of CAV systems is that they provide good, consistent ventilation in critical applications which require a high air exchange rate such as hospitals, labs, and clean rooms, gyms, auditoriums, etc. Some CAV systems are 100% fresh air (100% of return air is exhausted outside - no recirculation).

What circumstances are they used for? Pros and Cons?

*See above

And what exactly is an air handler? Someone told me that a furnace is an air handler, it makes sense, but I've never heard a furnace called that.

An air handler is a piece of equipment which supplies air for heating/cooling/ventilation to distribution (duct) systems.



Are there any websites or good books to help orientate me with CAVs? Thanks.

Try this - http://books.google.ca/books?id=UMk1EUp-W-UC&pg=PA237&lpg=PA237&dq=constant+air+volume+system+explained&source=bl&ots=gQTgjRY_Ka&sig=n4V5W8hGNHtrB064N_O1mHKnsVw&hl=en#v=onepage&q&f=false

[Antechs]

An air handler is a peice of equipment which supplies air for heating/cooling/ventilation to distribution (duct) systems.

Is a furnace a type of air handler?

Are CAV systems only for commercial applications?

What are some of the differences between CAV and residential systems?

How can I talk about a CAV system for 20 mins?
Thanks for the help

[amd]

Is a furnace a type of air handler?

Yes

Are CAV systems only for commercial applications?

Commercial and industrial mostly. (some mansions may have commercial style hvac systems)

Few residential systems are zoned, and the ones which are use very simple controls - no minimum ventilation position - just on/off, furnace/AC is staged or a bypass is used to prevent static pressure from getting too high)

What are some of the differences between CAV and residential systems?

->See first reply and draw your own conclusion.

[dandyme]

see if this does anything for you , if it's the correct file