ed home envelope are as tab-
ulated below:
Uo
value
zone
Maximum coefficient of heat transmission
1 .........
0.116 Btu/(hr.) (sq. ft.) (F).
2 .........
0.096 Btu/(hr.) (sq. ft.) (F).
3 .........
0.079 Btu/(hr.) (sq. ft.) (F).
(b) To assure uniform heat trans-
mission in manufactured homes, cav-
ities in exterior walls, floors, and ceil-
ings shall be provided with thermal in-
sulation.
(c) Manufactured homes designed for
Uo Value Zone 3 shall be factory
equipped with storm windows or insu-
lating glass.
[58 FR 55009, Oct. 25, 1993; 59 FR 15113, Mar.
31, 1994]
§ 3280.507
Comfort heat gain.
Information necessary to calculate
the home cooling load shall be provided
as specified in this part.
(a)
Transmission heat gains. Homes
complying with this section shall meet
the minimum heat loss transmission
coefficients specified in § 3280.506(a).
§ 3280.508
Heat loss, heat gain and
cooling load calculations.
(a) Information, values and data nec-
essary for heat loss and heat gain de-
terminations shall be taken from the
1989 ASHRAE Handbook of Fundamen-
tals, chapters 20 through 27. The fol-
lowing portions of those chapters are
not applicable:
21.1
Steel Frame Construction
21.2
Masonry Construction
21.3
Floor Systems
21.14
Pipes
21.16
Tanks, Vessels and Equipment
21.17
Refrigerated Rooms and Buildings
22.15
Mechanical and Industrial Systems
23.13
Commercial Building Envelope Leak-
age
25.4
Calculation of Heat Loss from Crawl
Spaces
(b) The calculation of the manufac-
tured homes transmission heat loss co-
efficient (Uo) shall be in accordance
with the fundamental principals of the
1989 ASHRAE Handbook of Fundamen-
tals and, at a minimum, shall address
all the heat loss or heat gain consider-
ations in a manner consistent with the
calculation procedures provided in the
document Overall U-values and Heat-
ing/Cooling Loads-Manufactured
HomesFebruary 1992PNL 8006, HUD
User No. 0005945.
(c) Areas where the insulation does
not fully cover a surface or is com-
pressed shall be accounted for in the U-
calculation (see § 3280.506). The effect of
framing on the U-value must be in-
cluded in the Uo calculation. Other
low-R-value heat-flow paths (thermal
shorts) shall be explicitly accounted
for in the calculation of the trans-
mission heat loss coefficient if in the
aggregate all types of low-R-value
paths amount to more than 1% of the
total exterior surface area. Areas are
considered low-R-value heat-flow paths
if:
(1) They separate conditioned and
unconditioned space; and
(2) They are not insulated to a level
that is at least one-half the nominal
insulation level of the surrounding
building component.
(d)
High efficiency heating and cooling
equipment credit. The calculated trans-
mission heat loss coefficient (Uo) used
for meeting the requirement in
§ 3280.506(a) may be adjusted for heating
and cooling equipment above that re-
quired by the National Appliance En-
ergy Conservation Act of 1987 (NAECA)
by applying the following formula:
Uo adjusted = Uo standard
×
[1+(0.6)
(heating efficiency increase fac-
tor)+(cooling multiplier) (cooling ef-
ficiency increase factor)]
where:
Uo standard = Maximum Uo for Uo Zone re-
quired by § 3280.506(a)
Uo adjusted = Maximum Uo standard ad-
justed for high efficiency HVAC equipment
Heating efficiency increase factor = The in-
crease factor in heating equipment effi-
ciency measured by the Annual Fuel Utili-
zation Efficiency (AFUE), or the Heating
Seasonal Performance Factor (HSPF) for
heat pumps, above that required by
NAECA (indicated as NAECA in for-
mula). The formula is heating efficiency
increase factor = AFUE (HSPF) home ¥
AFUE (or HSPF) NAECA divided by AFUE
(HSPF) NAECA.
Cooling efficiency increase factor = the in-
crease factor in the cooling equipment effi-
ciency measured by the Seasonal Energy
Efficiency Ratio (SEER) above that re-
quired by NAECA.
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Office of Asst. Sec. for Housing, HUD
§ 3280.509
The formula being cooling equipment=SEER
homeSEER NAECA divided by SEER
NAECA.
The cooling multiplier for the Uo
Zone is from the following table:
Uo
zone
Cooling multiplier (Cm)
1 .........
0.60 (Florida only).
1 .........
0.20 (All other locations).
2 .........
0.07.
3 .........
0.03.
(e) U-values for any glazing (win-
dows, skylights, and the glazed por-
tions of any door) shall be based on
tests using American Architectural
Manufacturers Association (AAMA)
1503.11988, Voluntary Test Method for
Thermal Transmittance and Condensa-
tion Resistance of Windows, Doors and
Glazed Wall Sections. In the absence of
tests, manufacturers shall use the resi-
dential window U values contained in
table 13 in chapter 27, the 1989 ASHRAE
Handbook of Fundamentals. In the
event that the classification of the
window type is indeterminate, the
manufacturer shall use the classifica-
tion which gives the higher U value.
For the purpose of calculating Uo val-
ues, storm windows shall be treated as
an additional pane.
(f)
Annual energy used based compli-
ance. As an alternative, homes may
demonstrate compliance with the an-
nual energy used implicit in the coeffi-
cient of heat transmission (Uo) require-
ment. The annual energy use deter-
mination must be based on generally
accepted engineering practices. The
general requirement is to demonstrate
that the home seeking compliance ap-
proval has a projected annual energy
use, including both heating and cool-
ing, less than or equal to a similar
base case home that meets the
standard. The energy use for both
homes must be calculated based on the
same assumptions; including assuming
the same dimensions for all boundaries
between conditioned and unconditioned
spaces, site characteristics, usage pat-
terns and climate.
[58 FR 55011, Oct. 25, 1993]
§ 3280.509
Criteria in absence of spe-
cific data.
In the absence of specific data, for
purposes of heat-loss/gain calculation,
the following criteria shall be used:
(a)
Infiltration heat loss. In the ab-
sence of measured infiltration heat loss
data, the following formula shall be
used to calculate heat loss due to infil-
tration and intermittently operated
fans exhausting to the outdoors. The
perimeter calculation shall be based on
the dimensions of the pressure enve-
lope.
Infiltration Heat-Loss=0.7 (T) (ft. of pe-
rimeter), BTU/hr.
where: T=70 minus the heating system capac-
ity certification temperature stipulated in
the Heating Certificate, in F.
(b)
Framing areas.
Wall .................................
15 percent of wall area less win-
dows and doors.
Floor and Ceiling .............
10 percent of the area.
(c)
Insulation compression. Insulation
compressed to less than nominal thick-
ness shall have its nominal R-values
reduced for that area which is com-
pressed in accordance with the fol-
lowing graph:
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