Simultaneous heating and cooling systems

Mechanical & Electrical Plan Vignette and Multiple Choice

Simultaneous heating and cooling systems

Postby abelur » Fri Dec 13, 2013 11:28 am

Really Need some clarity ....... Do I have my fundamentals correct here?

Question: Which of the following HVAC systems offer simultaneous heating and cooling?
Answers:
1) DX or Unitary System - YES, since each system controls only one zone or room
2) Single Duct, Constant volume system Single Zone - NO, since there is only one duct controlling each zone.
3) Single Duct, Constant volume system with Reheat - YES, since each zone has a reheat coil to control the air temperature.
4) Variable air volume (VAV) systems - NO, since temp and humidity are at a constant.
5) Dual Duct high velocity - YES since there are two ducts and each zone has a mixing box to control the air temperature.
6) Multi-zone System - YES, since there are two ducts and the air is mixed in the AHU before being transported to each zone.
7) All Water System - Hydronic System - YES, BUT true only for a 4 pipe systems as there are two supply pipes and it uses a fan coil in each zone/room to control the air temperature.
8) Air water system - YES. I don't know why
9) Air water Induction system - YES. I don't know why
10) Fan coil unit with supplementary air - YES. since there are two supply pipes and it uses a fan coil in each zone/room to control the air temperature.
11) Electric Systems - ?? I don't know.

Comments much appreciated!!
Thanks
abelur
 
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Re: Simultaneous heating and cooling systems

Postby CAlexandra06 » Sat Feb 15, 2014 8:14 am

1) DX or Unitary System - YES, since each system controls only one zone or room
ok

2) Single Duct, Constant volume system Single Zone - NO, since there is only one duct controlling each zone.
agree

3) Single Duct, Constant volume system with Reheat - YES, since each zone has a reheat coil to control the air temperature.
*NOTE that this system cannot efficiently heat and cool simultaneously. In practice it's only used where heating is rarely used, or when perimeter zone might need a little bit of heating compared to interior zone due to heat loss thru glass envelope.

4) Variable air volume (VAV) systems - NO, since temp and humidity are at a constant.
*Single duct VAV system cannot heat & cool simultaneously. But there is a multiple duct VAV system (ea zone has its own heating or cooling coil and a duct that serves the zone- this can heat & cool separate zones simultaneously. Can't heat & cool simult within the same zone. See Jennys notes.
To quote Kaplan: "It is impossible to simultaneously heat one room and cool another within the same zone, but different zones can be handled differently.")

5) Dual Duct high velocity - YES since there are two ducts and each zone has a mixing box to control the air temperature.
agree

6) Multi-zone System - YES, since there are two ducts and the air is mixed in the AHU before being transported to each zone.
agree that multi-zone can heat 1 zone while simultaneously cooling another

7) All Water System - Hydronic System - YES, BUT true only for a 4 pipe systems as there are two supply pipes and it uses a fan coil in each zone/room to control the air temperature.
*NOTE 3 pipe system can also heat and cool simultaneously. for 3 and 4 pipe, a thermostat at each room regulates the amount of water flowing thru each pipe.

8) Air water system - YES. I don't know why
The 2 types of air water system in Ballast are Induction system and Fan Coil with Supplementary Air. You cover these below.

9) Air water Induction system - YES. I don't know why
Induction system can heat and cool separate zones simultaneously, because each zone has its own induction unit with hot and cold water coils. Valves control amount of hot and cold water in each pipe. (Google "induction unit technical data dadanco pdf" for proof.)

10) Fan coil unit with supplementary air - YES. since there are two supply pipes and it uses a fan coil in each zone/room to control the air temperature.
agree

11) Electric Systems - ?? I don't know.
Ballast and Kaplan both talk about electric only for heating, not cooling, for what it's worth.
CAlexandra06
 
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Re: Simultaneous heating and cooling systems

Postby Corkscrewed » Fri Feb 21, 2014 9:24 pm

This thread is freaking priceless. Thank you!
User avatar
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Re: Simultaneous heating and cooling systems

Postby caharr02 » Sat Oct 11, 2014 12:46 pm

very helpful...bumping it to the top of threads
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Re: Simultaneous heating and cooling systems

Postby krisweeks » Thu Apr 07, 2016 8:28 pm

This is so much clearer than anything I've found in study materials. Thank you. I'm taking the test tomorrow, and I keep screwing up test questions over which systems are good for what. This helps a lot. :D
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Re: Simultaneous heating and cooling systems

Postby fio » Fri Apr 08, 2016 12:39 pm

YES it helps a ton (12,000 btus to be precise). I wish there were more threads like this! Thanks very useful.
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Re: Simultaneous heating and cooling systems

Postby tallow » Wed Nov 29, 2017 10:41 am

good post ... feels like it needs a bump.
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