6.6

7.1

6.5.3

Pressure Drop Across the Thermal Storage System. The static
pressure drop across the thermal storage system shall be,
measured with a manometer having an accuracy of 2.49 N/m2
(0.01 in. of water).

TIME AND MASS MEASUREMENTS

Time measurements and mass measurements shall be made to an
accuracy of +0.20% [3].

SECTION 7. APPARATUS AND METHOD OF TESTING

AIR AS THE TRANSFER FLUID

The relative position of the thermal energy storage system, the
temperature measuring instrumentation, the air flow measuring
apparatus and the reconditioning apparatus is shown in Figure Bla.
7.1.1 Test Ducts. The air inlet test duct, between the air flow
measuring apparatus and the thermal energy storage system,
shall have the same cross-sectional dimensions as the inlet
to the storage device. The air outlet test duct, between
the thermal energy storage system and the reconditioning
apparatus, shall have the same cross-sectional dimensions
as the outlet of the storage device.

7.1.2

Temperature Measurement Across the Storage System. A ther-
mopile shall be used to measure the difference between the
inlet air temperature and outlet air temperature of the
thermal energy storage system. It shall be constructed
from calibrated type T thermocouple wire all taken from a
single spool of wire. No extension wires are to be used
in either its fabrication or installation. The wire
diameter must be no larger than 0.51 mm (24 AWG) and the
thermopile shall be fabricated as shown in Figure B2. There
shall be a minimum of six junctions in the air inlet test
duct and six junctions in the air outlet test duct. These
junctions shall be located at the center of equal cross-
sectional areas.

An

The recommended apparatus consists of a closed loop configuration. open loop configuration is an acceptable alternative provided that the test conditions specified herein can be satisfied.

During all tests, the variation in temperature across the
air inlet and air outlet test ducts shall be less than
0.5°C (+0.9° F) at the location of the thermopile Junctions.
The variation shall be checked prior to testing utilizing
instrumentation and procedures outlined in reference [1].
If the variation exceeds the limits above, mixing devices
shall be installed to achieve this degree of temperature
uniformity. Reference [4] discusses the positioning and
performance of several types of air mixers.

The measuring junctions of the thermopile should be located as
near as possible to the inlet and outlet of the thermal energy
storage system. The air inlet and air outlet ducts shall be insu-
lated in such a manner that the calculated heat loss from
these ducts to the ambient air would not result in a tempera-
ture change for any test of more than 0.05°C (0.09° F) between
the temperature measuring locations and the storage system.

7.1.3 Dry and Wet Bulb Temperature Measurements. Thermocouples
or other devices giving a continuous reading shall be used
to measure the wet and dry bulb temperature at the locations
in the air inlet and air outlet ducts shown in Figure Bl.
ASHRAE Standard 41-66, Part I [1] shall be followed in mak-
ing these measurements.

7.1.4

Duct Pressure Measurements. The static pressure drop across
the thermal energy storage system shall be measured using a
manometer as shown in Figures B1 and B3. Each side of the
manometer shall be connected to four pressure taps that are con-
nected to an external manifold on the air inlet and air outlet ducts.
The pressure taps should consist of 6.4 mm (1/4 in.) nipples sol-
dered to the duct and centered over 1 mm (0.040 in.) diameter
holes. The edges of these holes on the inside surfaces of the
ducts should be free of burrs and other surface irregularities [5].

7.1.5 Air Flow Measuring Apparatus.

The air flow shall be mea

sured with the nozzle apparatus discussed in Section 7 of
ASHRAE Standard 37-69 [3]. As shown in Figure B4, this ap-
paratus consists basically of a receiving chamber, a dis-
charge chamber and an air flow measuring nozzle. The dis-
tance from the center of the nozzle to the side walls shall
not be less than 1 1/2 times the nozzle throat diameter, and
diffusers shall be installed in the receiving chamber at
least 1 1/2 nozzle throat diameters upstream of the nozzle
and 2 1/2 nozzle throat diameters downstream of the nozzle.
The apparatus should be designed so that the nozzle can be
easily changed and the nozzle used on each test shall be
selected so that the throat velocity is between 15 m/s
(2960 fpm) and 35 m/s (6900 fpm). Details on nozzle con-
struction and discharge coefficients that may be used are
contained in Section 7.3 of ASHRAE Standard 37-69 [3].

7.2

a

7.1.6

7.1.7

An exhaust fan capable of providing the desired flow rates
through the thermal energy storage system shall be installed
in the end wall of the discharge chamber. The dry and wet
bulb temperature of the air entering the nozzle shall be
measured in accordance with ASHRAE Standard 41-66, Part I
[1]. The velocity of the air passing through the nozzle
shall be determined by either measuring the velocity head
by means of a commercially available pitot tube or by mea-
suring the static pressure drop across the nozzle with a
manometer. If the latter method is used, one end of the
manometer shall be connected to a static pressure tap lo-
cated flush with the inner wall of the receiving chamber
and the other end to a static pressure tap located flush
with the inner wall of the discharge chamber, or prefera-
bly, several taps in each chamber should be connected through
a manifold to a single manometer. A means shall also be
provided for measuring the absolute pressure of the air in
the nozzle throat.

Air Leakage. Air leakage through the air flow measuring apparatus, air inlet test duct, the thermal energy storage system and the air outlet test duct shall not exceed 1.0% of the measured air flow.

The reconditioning apparatus

Air Reconditioning Apparatus.
shall control the dry bulb temperature of the air
entering the storage system to within + 1.0°C (+ 1.8 °F) of
the desired test values at all times during the tests.
Its
heating and cooling capacity shall be selected so that dry
bulb temperature of the air entering the reconditioning
apparatus may be raised or lowered by an amount equal to
the largest required in Section 8.

LIQUID AS THE TRANSFER FLUID

The test setup for thermal energy storage systems employing liquid as a transfer fluid is shown in Figure B5a.

7.2.1

Temperature Measurement Across the Storage System. The
temperature difference between the transfer fluid entering
and leaving the storage system shall be measured using
either two calibrated resistance thermometers connected
in two arms of a bridge or a thermopile made from
calibrated, type T thermocouple wire all taken from a
single spool of wire. The thermopile shall contain any
even number of junctions constructed according to the
recommendations in ANSI Standard C96.1-1964 (R 1969) [2].

An

The recommended apparatus consists of a closed loop configuration. open loop configuration is an acceptable alternative provided that the test conditions specified herein can be satisfied.

7.2.2

7.2.3

Each resistance thermometer or each end of the thermopile
is to be inserted into a well [6] located as shown in
Figure B5. To insure good thermal contact, the wells shall
be filled with light oil. The wells should be located just
downstream of a right angle bend to insure proper mixing [1].

To minimize temperature measurement error, the wells should
be located as close as possible to the inlet or outlet of
the storage device. In addition, the piping shall be insu-
lated in such a manner that the calculated heat loss from
this piping to the ambient air would not cause a temperature
change for any test of more than 0.05°C (0.090 F) between
each well and the storage system.

Additional Temperature Measurements. The temperature of the
transfer fluid at the two locations cited above shall also
be measured by inserting appropriate sensors into the wells.
ASHRAE Standard 41-66, Part I [1] shall be followed in
making these measurements.

Pressure Drop Across the Storage System. The pressure drop across the thermal energy storage system shall be measured using static pressure tap holes and a manometer. The edges of the holes on the inside surfaces of the pipe should be free of burrs and should be as small as practicable but not exceeding 1.6 mm (1/16 in.) diameter [5]. The thickness of the pipe wall should be 2 1/2 times the hole diameter [5].

7.2.4 Liquid Transfer Fluid Reconditioning Apparatus. The recon-
ditioning apparatus shall control the temperature of the
transfer fluid entering the storage system to within + 1.0°C
(+ 1.8°F) of the desired test values at all times during the
tests. Its heating and cooling capacity shall be selected
so that the temperature of the liquid entering the recon-
ditioning apparatus may be raised or lowered by an amount
equal to the largest required in Section 8.

7.2.5

Additional Equipment. A pressure gauge, a pump and a means of adjusting the flow rate of the transfer fluid shall be provided at the relative locations shown in Figure B5. In addition, a pressure relief valve and an expansion tank should be installed to allow the transfer fluid to expand and contract freely in the apparatusa.

a Figure B5 should not be interpreted to mean that the relief valve and expansion tank necessarily be located below the thermal energy storage unit.

a

SECTION 8. TEST PROCEDURE AND CALCULATIONS

The method that has been most commonly employed in testing of
water storage tanks in Japan [11, 12, 13] is to cause the transfer
fluid entering the storage device to undergo a step change
in temperature and to measure the temperature of the
transfer fluid leaving the storage unit. By integrating the
difference in temperature between the inlet and outlet over the
testing period and multiplying the result by the transfer
fluids' mass flow rate and specific heat, one can determine the
amount of heat added or removed during this time perioda. This
energy balance is shown conceptually in Figure B6 where the
area under the curve represents the energy absorbed during the
time period shown. If the time period chosen for the test were
some characteristic time depending upon the size of the storage
device chosen, the heat storage capability of different devices
could be compared. This will be illustrated by citing typical
results taken from reference [14].

Yang and Lee [14] performed an analysis to determine the nature
of the transient heat transfer between a heat storage unit and
a circulating or transfer fluid due to variations in the inlet
temperature of the transfer fluid. The configurations chosen
for analysis are shown in Figures B7, B8, and B9. Figure B7
shows a specific-heat type storage device in which a liquid
storage medium is heated or cooled by a fluid passing through
thin tubes inside the container. Figure B8 shows a pebble-bed
type unit in which the transfer fluid comes in direct contact
with the storage medium. Figure B9 shows as in Figure B7, a
heat-exchanger type storage device except in this case, the
transfer fluid is circulated around tubes which encapsulate a
latent-heat type material such as a salt hydrate.

The basic one-dimensional transient equations governing the
temperature distribution of both the transfer fluid and storage
medium are presented and solved using the Laplace transformation
technique. Yang and Lee point out that the boundary conditions
most appropriate to simulate a real storage device would be
some arbitrary variation of inlet fluid temperature with time.

This is strictly true only if the losses from the outside of the storage unit are negligible. Otherwise, the losses must be accounted for in the energy balance.