[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[EnergyPlus_Support] Re: Can we let supply air temperature float?
Dear Dr. Li,
Thanks for your reply. I guess I need to play with schedules in E+. Anyway, you said that there are several possible system implementations available. Can you point me to some sources or links? Or some search terms to search for? I want to read up on this, but couldn't find anything useful (I'm a newbie so I may not know the right terms).
Thanks!
Tim
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, YuanLu Li <yli006@...> wrote:
>
>
> I am not a HVAC building appraisor. I am responding only on operatin of equipment.If we can do the followings:
> 1)Turn off heat supply to the heating coil in the AHU, and let the supply air temperature float (uncontrolled);If you have intellegent control, this is possible. EPlus has economy cycle mode which use Outside air for increased ventilation, when the OD air temperature is at a suitable range.
> 2) Still run the fan to circulate air in the system. Still mix some fresh air from outside if required for ventilation; This depends on the building plan. The ducted air can always be circulated. VAV diffuser can change the amount of air flow at each diffuser (a veriable damper). The operation of these type of system always require some common computer control. The VAV diffuser itself can be self adjusting, as it can have duct and room temperature senser and a controller board in the unit, with a remote control to set the desired room temperature and move the damper. The controller and remote control is not simulated in EPlus.
> then we can extract excess heat gain from the first zones and redistribute it to the entire system. Some call this heat recovery. I usually like to use active heat control. For example, the heat from the light can be resecced into the false ceiling and collect as return air and treated separately. Printing room and other equipment can have ducts, so that the heat is vented out in Summer, and kept in in Winter. So we save energy and reuse free heat gain. Of course, after some time, when the zone temperatures decay below a threshold, we need to return to normal operation (controlled SAT). For simulation purposes, these ideas are already in Energy Plus, but the comptrollers and sensors are only inprepended as schedules and register values with set-point values, and calculated heat balance in each zone.
>
> IMy two questions:
> 1) Is this strategy practical and realizable in real systems? If not, why? Are there anything technically wrong?There are several possible system implimentation available.
> 2) In EnergyPlus, if I want to play with this idea, how can I turn off the heat supply to AHU and let the SAT float (while still running the fan)? In EPlus there is a dual band theremostat with a dead band temperature zone. Within the dead band, neither the heating nor cooling equipment would be ON. The fan can remail ON. However, high internal load can push the system into the cooling mode in Winter. It is not necessary to over cool and reheat, if this is not your choice.
> In Winter, you can let in outdoor air for cooling. However, some designer insisting on using the cooling sysem. The EPlus economy cycle mode do use the cold air and limit tis use to 5°C minimum in order to prevent the un-expected freezing of equipment and at the air inlet point. In EPlus, the VAV system can be operated without the reheat coil in the zone. Dr. Li
> To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> From: loveoflife219@...
> Date: Tue, 3 Apr 2012 19:34:28 +0000
> Subject: [EnergyPlus_Support] Can we let supply air temperature float?
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
> Hi all,
>
>
>
> I'm not an HVAC person, but a control engineer playing with HVAC control. So please excuse me if my questions are stupid :-)
>
>
>
> My main question is: is it possible to let the supply air temperature float (uncontrolled) some time during the day (not at night)? The details are as follows.
>
>
>
> Let's say we have a building in winter and the heating system is supplying hot air to the zones. The envelope is tight, so the heat loss to outside air is not very much. During the day, there is time when some zones have very high heat gain (from occupants, solar), even larger than their heat loss. Thus, even if the VAV boxes open at minimal level (for ventilation), or even closed, the net heat gain is still positive and the zone temperatures rise, which may cause discomfort. On the other hand, other zones have low heat gain, so they still require some heat load from the AHU.
>
>
>
> I understand that one solution to this issue is to always run the cooling system and supply chilled air to the VAV boxes, then reheat it at the terminal as required by each individual zone. However, I think this wastes energy, both because air is cooled then reheated, and because (free) excess heat gain in the first zones are not used.
>
>
>
> If we can do the followings:
>
> 1)Turn off heat supply to the heating coil in the AHU, and let the supply air temperature float (uncontrolled);
>
> 2) Still run the fan to circulate air in the system. Still mix some fresh air from outside if required for ventilation;
>
> then we can extract excess heat gain from the first zones and redistribute it to the entire system. So we save energy and reuse free heat gain. Of course, after some time, when the zone temperatures decay below a threshold, we need to return to normal operation (controlled SAT).
>
>
>
> My two questions:
>
> 1) Is this strategy practical and realizable in real systems? If not, why? Are there anything technically wrong?
>
> 2) In EnergyPlus, if I want to play with this idea, how can I turn off the heat supply to AHU and let the SAT float (while still running the fan)?
>
>
>
> Thank you very much!
>
> Tim.
>
------------------------------------
Primary EnergyPlus support is found at:
http://energyplus.helpserve.com or send a message to energyplus-support@xxxxxxxx
The primary EnergyPlus web site is found at:
http://www.energyplus.gov
The group web site is:
http://groups.yahoo.com/group/EnergyPlus_Support/
Attachments are currently allowed but be mindful that not everyone has a high speed connection. Limit attachments to small files.
EnergyPlus Documentation is searchable. Open EPlusMainMenu.pdf under the Documentation link and press the "search" button.
Yahoo! Groups Links
<*> To visit your group on the web, go to:
http://groups.yahoo.com/group/EnergyPlus_Support/
<*> Your email settings:
Individual Email | Traditional
<*> To change settings online go to:
http://groups.yahoo.com/group/EnergyPlus_Support/join
(Yahoo! ID required)
<*> To change settings via email:
EnergyPlus_Support-digest@xxxxxxxxxxxxxxx
EnergyPlus_Support-fullfeatured@xxxxxxxxxxxxxxx
<*> To unsubscribe from this group, send an email to:
EnergyPlus_Support-unsubscribe@xxxxxxxxxxxxxxx
<*> Your use of Yahoo! Groups is subject to:
http://docs.yahoo.com/info/terms/