Some Industry Perspectives on GasHeating RoofTop Units CEE Industry Partners Meeting September 26, 2

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Some Industry Perspectives on Gas-Heating
Roof-Top Units CEE Industry Partners
MeetingSeptember 26, 2007

• Jim Crawford
• Trane, Tyler, Texas

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Questions Posed by CEE

• 1. Is it feasible to make, market, and maintain a
  condensing furnace section in a weatherized
  appliance?  What would it require, and what are
  the likely cost impacts?
• 2. Where are the biggest savings opportunities
  considering modulating and condensing options?  
• 3. How do we address third party certification of
  these units which appear to currently fall
  between the cracks of ARI and GAMAs databases?
• 4. How do we achieve uniformity in energy
  efficiency measurements with AFUE, SSE, and TE
  currently being used?
• 5. Is it true that RTUs without modulation are
  unable to meet all three of the following ASHRAE
  standards  thermal comfort (55), ventilation
  (62.1) and efficiency (90.1)?

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A bit of Perspective

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A bit of Perspective

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Modern Roof Top Unit
Precedent 3-10 Ton
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The Numbers on Combustion

• CH4 2O2 CO2 2 H2O
• 16 64 44 36
• For each of CH4 burned, 2.25 1.08 quarts of
  H2O is produced 36/16 2.25
• Methane HHV 23,879 BTU/
• Methane LHV 21,520 BTU/
• Implied latent heat of vaporization of H2O
• Is 1048 BTU/

And that water is acidic, with a pH of about 4.
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The Thermal Path Through a Furnace

• Flame Temperature ca. 2000oF
• Entering the HX ca. 1000oF
• Leaving an 80 HX ca. 400oF
• Leaving a 90 HX ca. 110oF
• Leaving a 95 HX ca. 100oF
• Enter. Air Temp. ca. 70oF
• Lv Air Temp. for 80 ca. 120-150oF
• Lv Air Temp. for 90 as low as ca. 105oF

HX become much less effective as AFUE exceeds 80
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Dew Point of Natural Gas Combustion Products

• With 50 excess combustion air
• 50 RH
• 60oF
• 30 in HG
• The dew point of the combustion products is about
  125oF
• And the CO2 is about 7.5

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Air Power

• Circulation Generally sized for cooling at 400
  cfm/ton
• ARI AC default watts 365/1000 cfm
• Typical paired ratings _at_ 46oF rise
• 5 ton AC 100 KBTU/H 730W
• 20 ton AC 400 KBTU/H 2920W
• 100 ton AC 1,000 KBTU/H 7300W
• 80 induced draft blower 1/10th circ. blower
  power
• 90 induced draft blower 1/5th circ. blower
  power

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Condensing Rooftop Units ???

• 1. Q Is it feasible to make, market, and
  maintain a condensing furnace section in a
  weatherized appliance? 
• A At this point, it is possible but not
  feasible.
• Q. What would it require, and what are the
  likely cost impacts?
• A. As a manufacturer, I cannot discuss costs
  and prices, other than to say Nowhere near what
  CEE is quoted as having estimated.

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Spring 2007 CEE newsletter

• High-efficiency units cost in the
  30,000-40,000 range with a standard-efficiency
  model priced at about 12,000.

This is a rather extreme overstatement.
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2. Where are the biggest savings opportunities
considering modulating and condensing options?  

• Look at the performance specs, not the
  technology. Technology adds features, usually at
  added cost.

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3. How do we address third party certification
of these units which appear to currently fall
between the cracks of ARI and GAMAs databases?

• Smaller units are tested at ETL --- There is no
  crack.
• The largest units are made to order and are not
  available for a random draw for testing.
  Verification could be done by third-party
  oversight of manufacturers tests. Cost of very
  large units may warrant customer witness of tests.

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4. How do we achieve uniformity in energy
efficiency measurements with AFUE, SSE, and TE
currently being used?

• There should not be any confusion.
• AFUE is used on smaller products.
• SSE is used on larger products.
• TE does not seem to be used as a formal product
  specification.

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5. Is it true that RTUs without modulation are
unable to meet all three of the following ASHRAE
standards  thermal comfort (55), ventilation
(62.1) and efficiency (90.1)?

• Can un-modulated RTUs meet the requirements of
  ASHRAE-55, ASHRAE 62.1, and ASHRAE-90.1?
• Yes, Yes, Yes!
• Can pathological system designs or installations
  compromise performance?
• Yes.