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

[Bruce Easterbrook]

Actually ASHRAE 90.1 is the reference standard not 92.1
Bruce
On 09/08/2012 07:25 PM, Bruce Easterbrook wrote:
> 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 90.1 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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