[Equest-users] Cambridge direct fired units in warehouse space

[Bruce Easterbrook]

ASHRAE fundamentals has design information on stratification and on 
supply air throws etc.  You are getting into some pretty advanced 
modelling which eQuest won't do and your customer won't pay for.  Also 
remember the Cambridge sheet is done by marketers and advertisers not 
engineers.  I'm sure the unit will do much of what it claims but I don't 
think this is what you want to do if you are designing an energy 
efficient building.  You are going to be able to control the buildings 
air leakage with good design.  What you need initially is an idea of how 
much heat the building needs and how much fresh air.  A MUA unit is only 
used to temper the incoming fresh air and can be used for 
pressurization.  They are not used for heating.  Too much pressurization 
is a problem as well.  It doesn't necessarily reduce ACH, maybe a little 
if it is set up right and there is no wind.  A supply air fan can be 
configured with diffusers to give you a high velocity discharge which 
will mix the air in the building.  It will, if the air is released high 
enough also entrain some of the hot stratified air at the ceiling and 
bring it down with the main air flow.  This flow will drive down into 
the cooler air near the floor and mix.  This warmer air will also want 
to rise as it is less dense than the cooler air in the building and a 
circulation flow can be established.  I say can because generally a 
warehouse is full of racks floor to ceiling which will prevent this 
circulation pattern from happening.  You are going to have many dead 
zones which will need stratification fans.  You may not want all of 
these fans pushing air down.  You will need another form of heat 
independent from the MUA unit to provide the rest of the heat the 
building requires because heating a building with 100% OA is not 
efficient nor would regular building require this much fresh air.  
Consult ASHRAE 62.1 to determine how much OA that you need.  Consult 
SB-10 January 2012 of the OBC.  You will find it will reference ASHRAE 
92.1 with exceptions.  You must follow these codes.  They will also 
dictate your allowable lighting loads.  If you are dumping a lot of air 
then heat recovery becomes an option.  A warehouse can also have a lower 
heating set point which will reduce heat loss through the envelope.  
They typically don't have to be cooled.  But that brings up another 
problem, summer heat.  You need ventilation to remove heat.  Economizers 
work very well in Canada.  If you use a AHU with an economizer you don't 
need a MUA unit.  A warehouse is a building with tons of mass, over cool 
it at night with an economizer set at 100% exhaust, let the air stratify 
and exhaust the hot air off the bottom of the roof.  Go to minimum fresh 
air in the heat of the day and let the mass provide cooling.  
Stratification fans are not bad in the heating season as all the heat 
they make and energy they use stays inside the building.
This problem comes down to visualization.  You can calculate with 
reasonable accuracy if your supply fan discharge will get down to the 
floor.  If you do it at an isle crossing you will get 4 circulations in 
the isles.  Put a up-blast stratification fan between the supply air 
diffusers to assist.  Outboard areas require you to see the air flows 
and decide if an up or a down flow fan gives you the most benefit.  You 
can't rip the sheets off the order pickers clip board either.
With your auto size load at 300% you will need to determine why.  Check 
your people count, outside air and check infiltration.  Compare OA to 
62.1.  Check your envelope losses, compare them to the engineers heat 
loss.  When it comes to heat loss OA is the elephant.  Check all the 
eQuest defaults, many will have to be changed.
Bruce Easterbrook P.Eng.
Abode Engineering

On 09/08/2012 04:57 PM, Adam Barker wrote:
>
> Michael,
>
> The weather file is representative of the area, and I did run an auto 
> sized load, which calculated heating and airflow capacities much 
> higher than what was specified (about 3x higher on average off the top 
> of my head).
>
> You raise a good point regarding de-stratification -- reduced 
> stratification is another claim the company boasts, as the building is 
> pressurized. The claim to cut ACH due to infiltration in half.  I 
> believe the team is looking into reducing the # of de-stratification 
> fans in response to this.  I searched the forums for how to model 
> de-stratification about 2 weeks ago and came up with a few threads 
> basically hinting that it can't be accurately done. Does anyone have a 
> different opinion, or know if a way where this can at least be 
> approximated? I want to avoid playing with the infiltration rates as I 
> do not believe that is acceptable for a LEED model (at least here in 
> Canada it isn't). As of now I have not modeled this effect.
>
> The combustion problem is somehow managed through some limited 
> venting, though I can't remember exactly what is going on, which is 
> why I called them 'direct' fired units.
>
> *Adam Barker*, C.E.T., LEED AP BD+C
>
> Sustainability Project Manager
>
> Provident Energy Management Inc.
>
> T: 416-736-0630 x 1874 | abarker at pemi.com <mailto:abarker at pemi.com>
>
> *From:*Busman, Michael R [mailto:MBusman at chevron.com]
> *Sent:* Thursday, August 09, 2012 4:40 PM
> *To:* Adam Barker; 'equest-users'
> *Subject:* RE: Cambridge direct fired units in warehouse space
>
> Adam,
>
> I haven't had any experience with the Cambridge unit, nor am I able to 
> answer your question about the unmet heating hours.  Have you tried 
> auto-sizing just for a cfm and Btuh capacity comparison with the mech 
> engineer's load calc?  Also, is the weather file representative of the 
> warehouse location?
>
> Because the building is a warehouse, it triggered a question in my 
> mind that somebody else might be able to answer.  That is if eQUEST 
> models thermal stratification in high bay areas such as warehouses or 
> hangars?  If so, it may calculate unmet hours on the coldest days near 
> floor level and a nice warm temperature at ceiling/roof level.  Just a 
> wild thought.
>
> Mike Busman
>
> *Michael R. Busman, CEM*
>
> Lead Project Engineer II
>
> *Chevron Energy Solutions*
>
> A Division of Chevron U.S.A., Inc.
>
> 145 S. State College Blvd.
>
> Brea, CA  92821
>
> Direct 714-671-3561
>
> Fax 714-671-3438
>
> eFax 866-420-0335 (Include my Full Name followed by "CAI:MHTZ" on 
> Cover Sheet)
>
> Mobile 310-387-2083
>
> mbusman at chevron.com <mailto:mbusman at chevron.com>
>
> *From:*equest-users-bounces at lists.onebuilding.org 
> <mailto:equest-users-bounces at lists.onebuilding.org> 
> [mailto:equest-users-bounces at lists.onebuilding.org] 
> <mailto:[mailto:equest-users-bounces at lists.onebuilding.org]> *On 
> Behalf Of *Adam Barker
> *Sent:* Thursday, August 09, 2012 1:07 PM
> *To:* 'equest-users'
> *Subject:* [Equest-users] Cambridge direct fired units in warehouse space
>
> Hello everyone,
>
> I was recently asked to model the impact of Cambridge 'direct' fried 
> air handling units for a warehouse building compared to a conventional 
> MUA with supply and exhaust. Has anyone had experience with these units?
>
> They boast a very low fan power consumption (5 hp for 8565 cfm of 
> air), 92% thermal efficiency, and a temperature rise and max discharge 
> temp of 160 F.
>
> Most of the inputs are straightforward however I am not sure I am 
> modeling the 160 F temperature rise properly.  As of now I have 
> Packaged Single Zone systems and have entered 160 F as both the 'zone 
> entering max supply temp' and 'hot deck max leaving temp'. Would this 
> fully capture that temperature rise?  I ask as I am getting about 
> 150-200 unmet heating hours in these zones, even though all other 
> inputs are as per the mechanical engineer.  Is this significant, or 
> likely just the difference between how eQuest and the mechanical 
> engineer size their loads?  The building is a cold climate (southern 
> Ontario, Canada) LEED building, so I want to make sure I am modeling 
> as much benefit as possible.
>
> *Adam Barker*, C.E.T., LEED AP BD+C
>
> Sustainability Project Manager
>
> Provident Energy Management Inc.
>
> T: 416-736-0630 x 1874 | abarker at pemi.com <mailto:abarker at pemi.com>
>
>
>
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