What is constant flow system in air condioning (HVAC)?

[srinaath]

I am an electrical guy, i can't understand the concept of constant flow system...and how temperature is controlled in room by Air conditioner...thanks

 

[russ_watters]

Welcome to PF!

Your question is very vague: there are several types of constant flow systems, which can control temperature in several different ways:
1. By cycling the fan.
2. By controlling the amount of cooling done to the supply air.
3. By adding reheat.

Do you have a more specific description of the system you are dealing with?

 

[srinaath]

what i have read is that AC(air conditioner) is classified as constant flow and variable flow system...constant flow system is the one which maintains constant flow of water...what "water" and where?....then i have basic idea about vapor compression cycle....consider typical AC, initially it is OFF, now am turning it ON, i have set the temperature as 20 deg...what is happening actually after i set 20 deg,? how temperature is brought down to 20deg...PLEASE HELP ME OUT WITH THIS DOUBT... THANKS

 

[srinaath]

Welcome to PF!

Your question is very vague: there are several types of constant flow systems, which can control temperature in several different ways:
1. By cycling the fan.
2. By controlling the amount of cooling done to the supply air.
3. By adding reheat.

Do you have a more specific description of the system you are dealing with?

i am new to HVAC, can you tell me the types of constant flow system and why they are classified like that?? and can you elaborate the temperature control in each ways!...THANK YOU SO MUCH...

 

[russ_watters]

i am new to HVAC, can you tell me the types of constant flow system and why they are classified like that?? and can you elaborate the temperature control in each ways!...

I'm not sure what "classified" means...
1. Cycling is just what it means: the fan turns on and off based on a thermostat. Most residential systems work that way.
2. Controlling the amount of cooling done to the supply air is via cycling/modulating a refrigerant circuit or modulating a chilled water valve. That changes the supply air temperature. The downside to this is you don't get good dehumidification that way, so you need a separate method of dehumidification.
3. Reheat uses an electric or hot water heating coil to heat the air back up to maintain the temperature of the room after cooling it enough to ensure adequate dehumidification.

 

[srinaath]

I'm not sure what "classified" means...
1. Cycling is just what it means: the fan turns on and off based on a thermostat. Most residential systems work that way.
2. Controlling the amount of cooling done to the supply air is via cycling/modulating a refrigerant circuit or modulating a chilled water valve. That changes the supply air temperature. The downside to this is you don't get good dehumidification that way, so you need a separate method of dehumidification.
3. Reheat uses an electric or hot water heating coil to heat the air back up to maintain the temperature of the room after cooling it enough to ensure adequate dehumidification.

1.How fans control the temperature because fans are just responsible for air flow ?? (sorry that i ask so basic questions!)
2."by modulating refrigerant circuit" can you please explain deeply.. I mean how we are modulating and how it is done?....."modulating a chilled water valve"-->is this other type of system...? AND HOW??

AND PLEASE EXPLAIN BELOW QUESTIONS

(a)what is the basic layout of the air conditioning system
(b)what is constant flow system and variable flow system..
(c) what is the most commonly used temperature control method??
(d)temperature and humidity are inter related...so by controlling temperature i am controlling humidity right?
(e)how humidification/DE-humidification is done in typical AC??
(f)Should we also need to control pressure?

PLEASE CORRECT ME IF I AM WRONG...THANKS

 

[Ronie Bayron]

i am new to HVAC, can you tell me the types of constant flow system and why they are classified like that?? and can you elaborate the temperature control in each ways!...THANK YOU SO MUCH...

You may start with google. Search HVAC then have plenty of time to read, then come back to the forum, when you have done your part (study)

 

[srinaath]

You may start with google. Search HVAC then have plenty of time to read, then come back to the forum, when you have done your part (study)

ya i did some ground work by searching in google...but am not getting the clear picture...can you suggest me some books about basics of air conditioning

 

[Ronie Bayron]

ya i did some ground work by searching in google...but am not getting the clear picture...can you suggest me some books about basics of air conditioning

Click this HVAC

 

[russ_watters]

You may start with google. Search HVAC then have plenty of time to read, then come back to the forum, when you have done your part (study)

Yes, this is getting to be a pretty huge information request. You're basically asking us to write a book for you!

Is there a specific reason or problem behind this question that might help us focus it a little better?

Amazon has a lot of books. Here's one that might help:
https://www.amazon.com/dp/1619601990/?tag=pfamazon01-20

But again, without knowing the specific reason/focus of these questions, it is tough even to recommend the right book!

 

[srinaath]

Yes, this is getting to be a pretty huge information request. You're basically asking us to write a book for you!

Is there a specific reason or problem behind this question that might help us focus it a little better?

Amazon has a lot of books. Here's one that might help:
https://www.amazon.com/dp/1619601990/?tag=pfamazon01-20

But again, without knowing the specific reason/focus of these questions, it is tough even to recommend the right book!

hi, thanks for your advice , actually am an electrical engineer, recently working on HVAC systems... my role is to control the HVAC system.....i have read some basics about HVAC--> basic vapour compression cycle, types of AC present, how temperature is controlled by thermostat.
But i have doubt regarding humidification/de-humidification ( i have some knowledge about humdistat)..."In an ‘All-Air system’, the refrigerant or chilled water is used to cool and dehumidify the air in the air handling unit (AHU).(Source:http://www.electrical-knowhow.com/2012/03/in-previous-air-conditioning-system.html) i can't understand this statement...like how will refrigerant used to de humidify the air....is there any other method for humidify/de humidify (other than humidstat)......thanks in advance...

 

[russ_watters]

hi, thanks for your advice , actually am an electrical engineer, recently working on HVAC systems... my role is to control the HVAC system...

That's a difficult/unfair position you have been put in. Designing the controls for an HVAC system is the job of a mechanical engineer. It will take years of study and experience to turn you from an electrical engineer into a functional mechanical engineer.

But i have doubt regarding humidification/de-humidification ( i have some knowledge about humdistat)..."In an ‘All-Air system’, the refrigerant or chilled water is used to cool and dehumidify the air in the air handling unit (AHU).(Source:http://www.electrical-knowhow.com/2012/03/in-previous-air-conditioning-system.html) i can't understand this statement...like how will refrigerant used to de humidify the air..

When air gets cold, the moisture in it condenses out. It's what happens on the outside of a cold drink. That's the sole method of dehumidification of virtually all standard/general purpose HVAC systems.

...is there any other method for humidify/de humidify (other than humidstat)...

A humidistat is a controller - it doesn't do anything besides turning the de-humidifier on and off or modulating it. It isn't a de-humidifier itself. About the only other method of dehumidification used is absorbing the moisture with a desiccant.