I didn't have a chance to look at your model yet. I will do that when I go back to work on Monday, but let me give you an idea about energy savings with displacement ventilation and how to get them:
-Because supply air temperature is high (19 degree c) there will be more chances to use more free cooling if the outdoor conditions are suitable (cooling only savings).
Note: to do that you should have an economizer. -Because of the higher ventilation effectiveness of displacement ventilation, when the outdoor conditions are very hot, less outdoor flow could be used with DV which leads to energy savings as well (cooling and heating).
Note: you need to define that in the object (controller:outdoor
air).However .. these savings could be easily canceled, and even more energy use could happen because of:
1- The higher fan power due to higher flow rates with DV. This is because smaller d(t) between supply air and room set point requires higher flow to handle cooling loads. Note that the effect of increasing flow rate on energy use is cubical.
2- If there is a need for humidity control, the air will need to be cooled anyway for de-humidification which will cancel savings due to free cooling even if the outdoor temperature is suitable, unless another way of de-humidification other than cooling is used.
3- In the case of heating with 100% outdoor air, all heating inputs from the lighting are canceled. However, this is an advantage in the case of cooling with 100% outdoor air.
In conclusion if you want energy savings with DV you should :
-Have outdoor conditions
suitable for free cooling (dry and below 19 degree c)
-Or/and separate between thermal control and ventilation. e.g., use DV for ventilation only and use chilled ceiling for cooling.
-Or/and have a conditioned space that requires a very high ventilation rate due to high occupancy levels, e.g. class rooms
I hope that was useful
Cheers
Alaa Kandil
Calgary, Canada
From: "Lombe, Chilufya" <Chilufya.Lombe@xxxxxxxxxxxxxx>
To: alaak1974@xxxxxxxxx
Sent: Thu, July 1, 2010 7:00:34 AM
Subject: Re: Modelling Displacement Ventilation
Hi , thanks for replying to my post. I was expecting to get
lower energy usage for the displacement system. I have attached my idf files , I
followed the example files quite closely and went through the input/output
reference as well but I was expecting some kind of reduced energy usage from the
DV. To my knowledge , users donâ??t have control over the air velocity into
the room (except for PMV calcs) so the settings I change was only the supply
air temp (apart from adding the room air models).
10b.
Thu Jul 1, 2010 12:20 am
(PDT)
I have some experience with modeling displacement ventilation with energy plus
and I think I can help .. what kind of results did u get ? why do u think
results are strange ? what were you expecting?
Alaa Kandil
Calgary, Canada
________________________________
From: chilu32 <chilufya.lombe@xxxxxxxxxxxxxx>
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Sent: Thu, July 1, 2010 12:07:59 AM
Subject: [EnergyPlus_Support] Modelling Displacement Ventilation
Hi , I am trying to do a simple comparison between a displacement ventilation
system and a normal mixed zone system. The energy consumption numbers I get
back don't make sense and I am trying to troubleshoot my inputs. Anyone have
similar experience?? I added the room air models and changed supply air temp to
18C for the DV model.
_______________________________________________________________________________________
Chilufya Lombe
Electro-Mechanical Engineer
WSP Consulting Engineers SA Pty Ltd | P.O. Box 2613 | CAPE TOWN | 8000 | South
Africa
Tel: +27 (0)21 481-8649 | Fax: +27 (0)21 481-8799 | Cell: +27 (0)82 403-2024
e-Mail: chilufya.lombe@xxxxxxxxxxxxxx
www.wspgroup.co.za
_______________________________________________________________________________________
This email and all contents are subject to the following
disclaimer.
http://www1.wspgroup.co.za/disclaimer.htm
P Help save
paper - do you really need to print this email?