The conventional method of evaluating the performance of
insulation is to measure the R-value, the conductive heat flow resistance of
The measurement of conductive heat flow resistance is made using the guarded hotbox apparatus. This test procedure (ASTM C-518-02) measures the thermal conductivity of insulation material. In this test, one side of the specimen is heated to a specific temperature and after steady state heat flow has been reached, the temperature on the opposite side is measured. Through this temperature measurement the R-value is calculated. The outside surface of the test apparatus and the specimen is sealed and insulated to minimize the heat loss through the edge and eliminate the effects of any convection or radiant heat flow. This measurement solely defines the conductive heat flow resistance of the insulation material, the R-value.
Once the R-value of an insulation material is determined,
the heat flow through it can be calculated using Fourier’s steady-state heat
= A x ΔT
Q = Rate of heat flow, BTU/hr
A = Area, ft2
Temperature differential, ° F
R = Resistance to heat flow, hr.ft2 ° F/BTU
This equation is used to calculate
the benefit of increasing the thickness of any type of insulation as long as
there is no air movement (convective heat transfer) through the insulation.
As an example, consider 1000 ft2
of insulated area with a temperature differential of 40°F. Let
us include the outside air film at R-0.2 and the inside air film at R-0.7. The total R-value before the application of
any insulation is 0.9. Increasing the
insulation thickness by 1” increments at R-3.6/inch provides the following heat
flow rates as shown in Figure 1.1 & 1.2.
1.1: Percentage of total heat flow
Figure 1.2: Percentage of total heat flow reduction
In Figure 1.1, we can see that the
first 1” of insulation reduces the heat flow to 20% of the total and at 5” of
thickness, the heat flow is reduced further, down to 5% of the total. In looking at Figure 1.2, we see that
increasing the insulation thickness from 6” to 12” only provides an additional
heat flow reduction of 2%. Doubling the
insulation thickness (R-value); doubling the cost; only provides a modest 2%
increase in heat flow reduction. Based
on this observation, it is very difficult to justify the additional cost of
adding insulation thickness beyond 5”.
The Icynene Insulation System®
fills any shaped cavity and adheres to almost all materials, thereby, forming
an insulation layer with very low air permeance. Air flow is eliminated and for this reason,
conductive heat loss can be used as a sole criterion for establishing
insulation thickness with Icynene.
As shown in Figure 1.2, insulation
material with R-value of 3.6 per inch blocks out 95% of conductive heat flow
within the first 5 inches of the material.
Thickness beyond this point would bring more reduction in heat flow but
it would not be economically justified since the returns on additional R-value
have greatly diminished.
REDUCE AIR INFILTRATION - REDUCE ENERGY USE
REDUCE EQUIPMENT SIZE
In the case of insulation material
with significant air permeance, conductive heat loss should not be the only
criterion used for establishing insulation thickness. Convective heat loss must be considered as
well, particularly when a substantial latent load is involved.
Oak Ridge National Laboratory
(ORNL) conducted an experiment to
determine the efficiency of a roof assembly insulated with low density,
loose-fill fiberglass insulation and discovered that up to 50% of the heat loss
occurred as a result of convection; air circulation through the insulation. This result showed that the air-permeable
insulation had lost its anticipated thermal performance level by half and that
convective heat transfer had a significant negative impact on insulation
The importance of reducing air
infiltration can be easily demonstrated by analyzing the energy consumption for
heating and cooling hou
The first is a Typical house
designed according to the general building code requirements; with fiberglass
insulation, R-30 in the attic, R-19 in the walls and an air infiltration rate
of 0.7 ACH at natural pressure.
The second is a Better
version of this house with fiberglass insulation, R-43 in the attic and R-19 in
the walls and 0.6 ACH at natural pressure.
The third is an Icynene®
house with an insulation level of R-20 in the walls, R-20 in the ceiling and an
air infiltration rate of 0.1 ACH at natural pressure.
Heating and cooling costs and the
required heating and cooling equipment capacities for each house are plotted on
the following graphs. The utility rates
are set at $0.15 per kWh for electricity and $0.90 per Therm for natural
Figure 2.1 shows the energy costs
for heating in several different cities throughout
Figure 2.2 shows savings on
cooling costs with Icynene. They provide
savings of 25%~40% over the typical insulation system. The cities in a hot & humid climate show
greater savings due to the higher cooling demand.
As far as sizing heating and
cooling equipment is concerned, Icynene provides a significant reduction in
both heating & cooling load due to its air sealing property. Figures 2.3 & 2.4 show the equipment
size required in these hou
Icynene’s air seal capability
eliminates convective heat transfer within the insulation and reduces unwanted
air leakage through the building envelope.
This feature improves the efficiency of the building envelope thereby reducing
the heating and cooling costs and reducing the size of HVAC equipment as
outlined in figures 2.1 through 2.4. As
a result lower operating costs are realized and the cost of the operating
equipment is reduced.
Often, air permeable insulation at twice the
R-value gets used and still comes short of the desired energy savings as shown
in Figures 2.1 and 2.2.
The on-site spray applied
application of Icynene provides an excellent air seal that ensures a low air
infiltration rate for the building envelope.
This quality improves energy efficiency of the building as demonstrated
through the graphs above and in addition, the overall performance of the
building resulting in better sound attenuation, healthier indoor environment
and enhanced thermal comfort.