National energy savings potential in HUD-code housing from thermal envelope and HVAC equipment improvements

ASHRAE Transactions, July, 2007 by Robert Lucas, Philip Fairey, Robert Garcia, Michael Lubliner

The analysis was conducted using a DOE-2 (LBNL 1981) hourly simulation residential energy analysis software program called EnergyGauge[R] USA, version 2.5 (FSEC 2006). The EnergyGauge analysis assumptions are provided in Table 1. Duct insulation values are all R-8 except for HUD (R-4) and ENERGY STAR (R-6).

Table 1. EnergyGauge USA Analysis--Thermal Input Assumptions

City and          [U.sub.o] Analyzed         Floor/Ceiling/Wall
Thermal     (Btu/h*[ft.sub.2]*[degrees]F)        R-Value
Efficiency
Level

Houston

HUD (1994)              0.116                     11/30/11

NFPA                    0.098                     11/28/11
(2005)

IECC                    0.097                     13/30/13
(2006)

ESTAR                   0.087                     11/30/11
(2004)

Best                    0.056                     33/38/21
Practice

Raleigh

HUD (1994)              0.095                     11/30/11

NFPA                    0.089                     14/28/11
(2005)

IECC                    0.067                     19/38/13
(2006)

ESTAR                   0.084                     11/33/13
(2004)

Best                    0.056                     33/38/21
Practice

Chicago

HUD (1994)              0.078                     22/30/11

NFPA                    0.073                     22/33/13
(2005)

IECC                    0.062                     25/38/19
(2006)

ESTAR                   0.059                     33/36/19
(2004)

Best                    0.056                     33/38/21
Practice

City and    Fenestration  Glazing     Air         Duct Leakage
Thermal       U-Factor      SHGC     Exchange       Rate (25
Efficiency                  (1)    Rate (ach     PA/[ft.sub.2])
Level                                (2) at 50
                                        PA)

Houston

HUD (1994)          1.10     0.70        9.0      Qn = 12%

NFPA                0.52     0.60        7.0      Qn = 7%
(2005)

IECC                0.75     0.40        7.0      Qn = 9%
(2006)

ESTAR               0.38     0.40        7.0      Qn = 5%
(2004)

Best                0.34     0.40        4.0      Qn = 3%
Practice

Raleigh

HUD (1994)          0.52     0.60        9.0      Qn = 12%

NFPA                0.52     0.60        7.0      Qn = 7%
(2005)

IECC                0.40     0.40        7.0      Qn = 9%
(2006)

ESTAR               0.38     0.40        7.0      Qn = 5%
(2004)

Best                0.34     0.40        4.0      Qn = 3%
Practice

Chicago

HUD (1994)          0.52     0.60        9.0      Qn = 12%

NFPA                0.52     0.60        7.0      Qn = 7%
(2005)

IECC                0.35     0.55        7.0      Qn = 9%
(2006)

ESTAR               0.38     0.40        7.0      Qn = 5%
(2004)

Best                0.34     0.40        4.0      Qn = 3%
Practice

(1) Conversations and e-mail correspondence with R. Garcia, Fleetwood
Housing Division, Riverside, CA, 2006.
(2) ach = air changes per hour.

PROTOTYPE DESCRIPTION

A typical 56 ft double-section three-bedroom manufactured home prototype with 12% glass-to-floor area was used in this study. Previous HUD-code related research efforts have used this same prototype, which is generally accepted as representative of the majority of HUD-code homes (Conner et al. 1992; Conner et al. 2004). In 2005, double-section homes represented roughly 80% of the market share.(1) The vented roof has typical dark asphalt shingles and is built using flat 2 x 2 ft roof trusses 24 in. on center. Insulation is assumed to be blown and tapered at baffled eave vents. The 2 x 6 framed, 24 in.-on-center floor is located over a vented crawlspace with blanket/batt floor insulation located in the "belly" and compressed at the I-beams. The walls are assumed to be 16 in. on center and 2 x 4 for the R-13 and R-11 batt insulation cases and 2 x 6 for the R-19 and R-21 batt insulation cases. The doors and windows are industry representative and available models, with the exception of the IECC case, which assumes the prescriptive U-factor requirements of 0.75, 0.4, and 0.35 Btu/h*[ft.sup.2]*[degrees]F for the three cities examined. Electric domestic water heating with 50-gallon tanks located in the conditioned space with an energy factor of 0.90 are assumed for all cases. Table 1 provides the prototype assumptions used in the analysis.