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Economizers requriements 503.3.1
June 27, 2017
2:39 pm
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Eric.sowers@cdhpartners.com
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June 27, 2017
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This is very big issue for us right now, would love to hear a ruling on this.

I agree it seems the building is limited to a maximum of 480,000 btuh of non-economizer equipment (each of these should be 54,000 btuh or less) and so in the building above at 600,000 btuh: 120,000 btuh worth of equipment in the building will have to be ON economizer.

This is a significant problem in a building full of VTAC, VRV or other similar small, packaged units which have no economizer capability in the industry.

If the code is trying to restrict the use of this equipment, they should state it simply, "thou shalt not use VTAC equipment on buildings over 40 tons".

Look forward to some response here.

August 13, 2014
3:53 pm
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chad fikes
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August 13, 2014
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I have a very similar issue with 503.3.1.  I have a multi unit apartment building (120 units) in climate zone 4A.  Each apartment unit has a 1.5 ton furnace/condensing unit system.  I'm being required to run the ComCheck software and my building fails due to foot note "a".  The total of the individual systems is 2,160,000 Btu's which is well above the 300,000 Btu allowed by foot note "a".  Is the IECC really going to make me put an econmomizer on every residential furnace over the 300,000 BTU limit?  Is there an exception in the code that I'm missing somewhere?  Please, any feed back will be very appreciated.

March 21, 2014
11:52 am
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hvac guy
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March 21, 2014
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I was told the same thing. In my case I have two separate rooms each with their own split system (each 3 ton) and because there is a 3'wide opening in the wall separating the two rooms that this small opening is interpreted now as ONE large open room. Because they interpret it as being one large room, the two systems combined is greater than 5 tons and both require economizers. I too do not feel this is the intent of IECC. The code should not allow this type of interpretation.   

May 28, 2013
5:56 pm
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malcolm knight
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May 28, 2013
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I can't believe there has not been more discussion on this.  I too think footnote "a" is interesting.  However, I interpret it differently.  I'm in climate zone 3A - warm and humid.  I read 503.3 to require economizers on systems in accordance with 503.3.1(1).  That table requires economizers on systems with a capacity greater than or equal to 54kBtuh.  All systems smaller than that do not require economizers.  Footnote "a" only refers to systems with capacity greater than 54kBtuh and I read it as saying that I can have up to 480,000 Btuh of systems greater than 54 kBtuh capacity or 20% of my required economizer capacity without economizers, whichever is greather.  Section 503.3 says that if I have a room with a load greater than 54 kBtuh and use multiple systems I have to use the aggregate capacity of the systems to make the economizer determination.  However, I do not read it to say that if my building has an aggregate load greater than 480 kBtuh I have to provide economizers on all systems above the 480 kBtuh threshold.  For example, I do not see where this would require a 500 room hotel with 500 1-ton PTACs (one per room) to require economizers on 460 of the PTACs, or if I have a k-12 school with 100 classrooms with 100 2-ton water source heat pumps to require economizers on 60 of them.  The small equipment provides very good capacity control - when no one is in the room the unit can be off or setback and I'm not going to get in trouble because a small unit with a failed economizer in a warm and humid climte starts growing nasty stuff in my building.  Also, the commentary for the 2009 IECC on this issue provides no guideance.  I teach an IECC course and this question gets brought up all of the time.  I think the IECC needs to be more specific on the application of this table.  The wrong application of this table along with things like supply air temperature reset and duct static pressure rest combined can wreak havoc on an HVAC system and a building in a warm and humid climate.  Control systems are already too complicated for the average small building owner.

December 22, 2011
3:23 pm
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mbeavers@normal.org
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The footnote (a) to this code section is interesting to me.  The word "building" throws me off.  Let's take for example a 4 story building.  The cummulative load for the entire building is 600,000 btu's.  There is no space (zone) within the building over 48,000 btu's.  The footnote (a) would require the units to have economizers, I presume, because of the overall load of 600,000.  This is the case, even though the spaces do not communicate with one another. 

Is this the way you would interpret?

December 13, 2011
4:21 pm
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joseph moore
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October 16, 2011
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I have been involved extensively with the Energy Code for over 10 years. I respectfully disagree with the interpretation the State has given you.

If the room or space is supplied by only one unit and the size of that unit is less than 54,000 Btu/h that unit is exempt from the economizer requirement. (Table 503.301(1)) The code does not regulate the return air design for the room or space.

Footnote a to the table adresses multiple units in a building and limits the total capacity of units without economizers to 400,000 Btu/hr per building or 20% of it's air economizer capacity, whichever is less.

I hope this helps.

December 2, 2011
12:24 pm
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dave feldbruegge
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December 2, 2011
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Informed from a Wisconsin State head reviewer that even thou 503.3.1 states "Where a single room or a space is supplied by multiple air systems, the aggregate capacity of those systems shall be used in applying this requirement"  that there interpretation is that if the return air of systems are combine, even thou rooms are not being supplied by multiple systems than aggregate must be used.

Explanation is that the shared return air becomes supply air so therefore you now have a shared system.  Is this intent and if so than for future code they should omit the supplied by a single room or space terminology and state combined sysetms to be more clear.