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NRC Solar Monitoring Program
NRC SOLAR MONI'FOHING PROGRAM
by
S . A . Barakat, W.E. Carscallen and B . E . S i b b i t t
1. INTRODUCTION
A major o b j e c t i v e of the s o l a r energy program in Canada is t h e g a t h e r i n g of d a t a on t h e performance o f s o l a r h e a t i n g systems by monitoring so lax i n s t a l l a t i o n s . F o l l o w i n g c o l l e c t ion, a n a l y s i s and evaluation, t h e d a t a a r e used to determine the thermal and mechanical performance of a s o f a r heating system and i t s subsystems and to formulate
d e s i g n guidelines. The extent o f monitoring f o r any one installation depends primarily an the subsequent use t o b e made o f t h e data.
In general, information obtained from m o n i t o r i n g can b e used t o address one or Inore o f the f o l l o w i n g o b j e c t i v e s :
-
to describe t h e over-all thermal performance of a s o l a r system intcms of its c o n t r i b u t i o n to t h e energy needs of a s p e c i f i c
b u i l d i n g ,
- t o v a l i d a t e solar heating system computer simulation programs,
t o permit d e t a i l e d a n a l y s i s of t h e pesformance of a s o l a r h e a t i n g
system,
which
inturn
will i d e n t i f y shortcomings in system d e s i g n ( e . g . , oversized storage, i n c o r r e c t c o n t r o l operation), componentweaknesses, and shartcomings in component disposition and
i n s t a l l a t i o n in the b u i l d i n g (subsequent analysis can a l s o be c a r r i e d out to indicate t h e performance improvement t o b e expected
f r o m modifications of rhe s o l a r system! t h i s should l e a d to d e s i g n g u i d e l i n e s for s o l a r heating systems as w e l l as recommendations f o r component manufacturing, installation and maintenance).
-
to validate combined s o l a r and b u i l d i n g heat l o s s computer simulation programs.2 . MONITORING PROGRAM
2.1. Performance Factors
Some o f the f a c t o r s used to describe the thermal performance o f a
solar h e a t i n g system and its subsystems are defined below. Reference
should b e made to Figure 1, which shows a t y p i c a l liquid solar heating
system.
*
2 . 1 . 1 - F r a c t i o n s o l a r , FS, represents t h e solar energy c o n t r i b u t i o n to
t h e net heating requirement (space and service water h e a t i n g ) a f t h e
b u i l d i n g
It can be subdfvided into t h e fraction s o l a r
f o r
space h e a t i n g[QS/Q1) and the f r a c t i o n s o l a r f o r service water h e a t i n g (QWS/Q14W]. The net space h e a t i n g demand of the b u i l d i n g can be o b t a i n e d in 3 number of
ways :
-
by measurrrnent o f QS
ands,
(s
=QS
+ QA),
-
by comparison w i t ha
s i m i l a r non-solar b u i l d i n g f o r which purchased energy is measured, i .e.
,
f o r whichQH
= QA,-
by a n a l y s i s , using a building heat loss model to account forL ~ ' QP and
QIG,
(QH = LB-
(s
+PIG))
- b y d e t a i l e d measurement where most losses and g a i n s c o n t r i b u t i n g
t o
LB,
C$ and QICare
measured and t h e remainder c a l c u l a t e d .2.1.2. Heating system utilization e f f i c i e n c y ,
~ K S ,
is t h e r a t i o of t h es o l a r energy utilized to t h e amount c o l l e c t e d , and a measure a l s o of t h e h e a t l o s s e s of the
sysrem
2 . 1 . 3 . Collector array e f f i c i e n c y , q ~ , is the r a t i o of t h e energy collected b y t h e array to t h a t i n c i d e n t on it. This accounts f o r a r r a y losses as well as variation of i n s o l a t i o n d u r i n g the measurement period. It s h o u l d t h e r e f o r e
be
distinguished froan t h e instantaneous c o l l e c t o r e f f i c i e n c y reported by mnufacturers and t e s t agencies2.1.4. Over-all s o l a r system conversion e f f i c i e n c y , q,, is t h e r a t i o
of the s o l a r energy utilized to the solar energy i n c i d e n t on the c o l l e c t o r a r r a y
This r e p r e s e n t s t h e e f f i c i e n c y with which t h e solar system converts solar r a d i a t i o n to u s a b l e energy. It can a l s o b e expressed as
The f i r s t parameter, FS/Ac, characterizes t h e s o l a r system design; t h e second,
(%
4%)
/Ic, characterizes the h u i l d i n g h e a t i n g load, h o t waterusage, and weather.
2.1.5. Storage subsystem e f f i c i e n c y , 0
S
Storage efficiency is an i n d i c a t i o n o f the energy l o s s characteristic of t h e s t o r a g e u n i t .
Other performance factors may be of importance in some applications, including heat exchanger effectiveness and heat pump coefficient of
performance,
if
applicab le.
2.2 Levels o f Monitoring
A number of solar heated b u i l d i n g s were equipped with m n i t o r i n g
systems, the level of monitoring d i c t a t e d b y t h e type of building and
t y p e of solar heating system a s w e l l as by t h e use to b e made of the data. It must b e recognized t h a r r e f i n e d d a t a can only b e obtained by means of
an increase in t h e c o s t of instrumentation, maintenance, and subsequent data monitoring
and
processing. Monitoringlevels
a r e summarized as follows :2.2.1. Level 1
The consumption o f conventional o r purchased e n e r g y only ( i . e . , e l e c t r i c i t y , gas
o r
o i l ) is measured. The n e t heating requirement isinferred by a n a l y s i s o r comparison w i t h a s i m i l a r non-solar-heated
b u i l d i n g . T h i s l e v e l w i l l provide a rough estimate of f r a c t i o n s o l a r and
is s u i t a b l e f o r privately-funded solar-heated installations f o r w h i c h
c o s t l y m o n i t o r i n g instrumentation cannot b e j u s t i f i e d . It i s a l s o the
a p p r o p r i a t e l e v e l of monitoring f o r funded projects t h a t are duplicates
of o t h e r s monitored in more detail arid at a higher l e v e l ( e . g .
,
a row-housing group c o n t a i n i n g a number of i n d i v i d u a l solar s y s t e m s ) .
2.2.2. Level 2
T h i s level of monitoring addresses t h e f i r s t o b j e c t i v e of m o n i t o r i n g ,
a s w e l l a s t h e second and third o b j e c t i v e s ( s e e S e c t i o n
1.1,
to a degree t h a t dependson
t h e monitoring instrumentation and d a t a acquisition equipment used. It can b e d i v i d e d i n t o two c a t e g o r i e s according to t h ed a t a o u t p u t device and frequency o f measurement and r e c o r d i n g of data; t h e f i r s t u s e s i n t e g r a t i n g h e a t meters, t h e second, an automatic d a t a a c q u i s i t i o n s y s tern.
[a) An integrating heat meter is a d e v i c e t h a t receives a n a l o g u e
signals from Two temperature s e n s o r s (temperature difference) and a f l o w
sensor, and is calibrated to measure t h e i n t e g r a t e d h e a t flow p a s t a
point i n the system. [More details o f the meter and a s s o c i a t e d
instruments are presented in S e c t i o n 3 . 1 1 , I n t e g r a t i n g h e a t meters are
used at d i f f e r e n t p o i n t s in the s o l a r system to measure the amounts of
s o l a r energy c o l l e c r e d [QC], solar energy delivered t o space (Q)
,
and s o l a r e n e r g y used for hot w a t e r p r e h e a t i n g((lws)
as well as any o t h e r h c n tflow q u a n t i t i e s r e q u i r e d for the a n a l y s i s o f a p a r t i c u l a r subsystem. I n a d d i t i o n , i n t e g r a t i n g meters are used to measure purchased energy
[QA and & A ) , and an i n t e g r a t i n g pyranometer i s used to measure solar energy i n c i d e n t on the c o l l e c t o r s [ I )
.
C
I n t e g r a t e d energy values a r e generally recorded on a weekly or
month1 y b a s i s ; more f r e q u e n t reading is impractical. I n t e g r a t e d data arc s u i t a b l e for gross analysis o f sys tern and component performance (weekly
and monthly values of FS, r~~~~~
,
.
. .
and f o r validating seasonalsolar system simulation programs such as FCHART and S o l c a s t .
(b] E x p e r t m e n t a l s o l a r systems and systems w i t h novel. f e a t u r e s of components ~ e q u i r e d e t a i l e d data for dynamic system and component
performance analysis. D e t a i l e d performance d a t a are a l s o r e q u i r e d for
v a l idarion of s o l a r sys tern simulation programs such as WAI'SUN a n d TRNSYS
.
F o r s u c h d e t a i l e d data gather in^ ( t h a t is, data col l e c t c d on an h o u r l y o r quarter-hourly basis) an automatic data acquisition and l o g g i n g system is r e q u i r e d . A similar data sys tern can be used i n (a] above i f t h enumber o f integrating meters becomes p r o h i b i t i v e and data h a n d l i n g
T h i s monitoring system a l s o utilizes temperature and flow sensors, b u t a l l readings are recarded by a d a t a logger or a minicompt~ter, both of which are capable o f r e c o r d i n g a large number o f r e a d i n g s in v e r y s h o r t
time intervals. A data logger performs a m i n i m u m of p r o c e s s i n g on t h e
data p r i o r to storing in a way s u t t a b l e for f u t u r e computer processing
(e.g., on magnetic tape). A minicomputer, on the o t h e r hand, has t h e
additional c a p a b i l i t y of on-site processing and reducing data to f i n a l form ( i . e . , energy quantities and p e r f o m n c e f a c t o r s ) ,
2.2.3 Level 3
T h i s l e v e l c o n s t i t u t e s measurement of t h e elements o f t h e b u i l d i n g
energy requirement as well as those
of
t h e solar system. The measured q u a n t i t i e s are the same as those in Level 2 [Ic, Qc, Q ,a,
Qvs.. .) plust h e building-related energy values (LB, Qp, and QIG). An automatic data a c q u i s i t i o n and l o g g i n g system
is
used. T h i s level of monitoring is required for v a l i d a t i o n of combined solar-system and b u i l d i n g heat l o s s simulation programs. There are c u r r e n t l y no s o l a r - h e a t e d b u i l d i n g s w i t h this l e v e l o f monitoring.It should b e noted t h a t because of t h e close-coupling o f t h e solar system and the b u i l d i n g in a passive solar heating application t h e
monitoring af such i n s t a l l a t i o n s is extremely difficult, Full monitoring can o n l y b e achieved w i t h Level 3 . The a l t e r n a t i v e is to r e l y on Level 1 monitoring. A summary of solar-heated b u i l d i n g s now being monitored
b y DBR or undergoing i n s t a l l a t i o n of a monitoring system is given i n
Tab Ee I . The level of monitoring of each of the projects is a l s o given.
3 .
MONITORING
OF NRCSINGLE-FAMILY
SOLAR DEMONSTRATION HOUSES3 . 1 . Equipment
Monitoring systems corresponding to Level 2(a) w e r e installed in the
summer and f a l l o f 1 9 7 7 in twelve of t h e f o u r t e e n NRC s o l a r d e m o n s t r a t i o n
houses across Canada (1). They incorporate a v a r i e t y of liquid and a i r
solar systems, some w i t h heat-pump assistance. A t y p i c a l m o n i t o r i n g arrangement i s shown in Figure 2. F o r subsystems i n which energy is t r a n s f e r r e d b y a heat t r a n s f e r medium (air or liquid), a n i n t e g r a t i n g
heat meter was used to measure the i n t e g r a t e d v a l u e s of h e a t flow and
f l u i d flow to or from the subsystem. It accepts analague signals f r o m two t e m p e r a t u r e sensors and a flow sensor, and displays i n t e g r a t e d energy
value in MTh and i n t e g r a t e d f l u i d f l o w in m3. A f a c t o r proportional t o
the product of d e n s i t y and specific heat o f water is b u i l t i n t o the electronics of the meter. It is, t h e r e f o r e , necessary to c a l i b r a t e t h e meter if it is to b e used w i t h f l u i d s o t h e r than water.
P r e c i s i o n platinum rssis tance thermometers [RlQ 3s) were used for temperature measurement. They have a nominal resistance o f 100 fi a t O O C
and a thermal c o e f f i c i e n t of resistance of 0.00385
R/Q/"c.
TheRTD
swere
interchangeable w i t h i n 0, O S D C over t h e range 20 to 9 0 ' ~ .A s b o t h l i q u i d a n d air systems were monitored, two types o f flow meter were selected. L i q u i d flows were measured w i t h a p o s i t i v e -
displacement n u t a t i n g disc flow meter equipped with an impulse head to y i e l d one pulse (switch closure) f o r every 10 L of l i q u i d passing through
t h e meter. T h i s p u l s e output was fed i n t o the i n t e g r a t i n g h e a t meter.
The i n t e g r a t e d flow could also b e read o f f a d i g i t a l counter. Air flows were measured w i t h a propeller-type vane anemometer. The o u t p u t o f t h e vane anemometer w a s in t h e form o f an a-c signal of v a r i a b l e frequency
t h a t depended on t h e r o t a t i o n a l speed o f the v a n e and hence on t h e a i r
v e l o c i t y o r air flow r a t e , An e l e c t r o n i c i n t e r f a c e was p r o v i d e d b e t w e e n
the anemometer and t h e i n t e g r a t i n g heat m e t e r to p r o v i d e t h e meter w i d 1 the p m p e r p u l s e i n p u t .
For subsystems having energy i n p u t s in the farm of a c o n v e n t i o n a l
energy source
(i.e
.
,
a i l , gas or e l e c t r i c i t y ) alternate measuring schemes were u t i l i z e d . The auxiliary energy c o n t r i b u t i o n of an o i l or gasfurnace was estimated from t h e measured fuel consumption and an assumed
furnace e f f i c i e n c y . Gas consumption was measured w i t h a d i s p l a c e m e n t gas
meter, Oil consumption was calculated using the furnace n o z z l e size and
the measured elapsed on-time o f t h e furnace. The l a t t e r was measured w i t h a totalizing clock. The electric e n e r g y consumption was measured w i t h klVh meters with the output d i s p l a y e d on five d i a l s , b u t t h e s e were
l a t e r changed t o a digital o u t p u t because many of the monitoring agents
experienced difficulty
i n
reading the d i a l comb inatians.
For measurement of energy f l o w s in circuits where t h e temperature l e v e l s remained relative1 y c o n s t a n t bemeen measurements [one week), o n l y
t h e f l u i d flow w a s i n t e g r a t e d and the temperature d i f f e r e n c e measured a l o n g w i t h the o t h e r parameters on a weekly basis. Energy flow was
calculated using the average temperature d i f f e r e n c e and the i n t e g r a t e d
f l u i d flow. T h e e n e r g y demnd f o r domestic h o t water h e a t i n g systems was
determined in t h i s way because s h e warer mains temperature and t h e hot
water supply temperature [ s e t to a fixed value) could b e assumed c o n s t a n t
in t h e i n t e r v a l between readings. A commercial e l e c t r o n i c thermometer
was used, c o n s i s t i n g of three t h e r m i s t o r s connected to a r e a d o u t t h r o u g h
a three-channel selector.
S o l a r r a d i a t i o n i n c i d e n t on the collector array w a s normally estimated using values obtained from the nearest r a d i a t i o n measuring
s t a t i o n . I f these was
no
s t a t i o n nearby, a pyranometer was mounted att h e site at t h e same slope as the c o l l e c t o r s and w a s connected 60 an
i n t e g r a t o r to g i v e a continuous d i g i t a l readout o f t h e i n t e g r a t e d solar r a d i a t i o n .
3 - 2 . C a l i b r a t i o n and I n s t a l l a t i o n
C a l i b r a t i o n and i n s t a l l a t i o n of t h e monitoring equipment were carried out b y NRC s t a f f ; o n - s i t e plumbing and e l e c t r i c a l m o d i f i c a t i o n s of the
solar s y s t e m to prcpare it t o accept t h e equipment were performed b y t h e
local plumbers and e l e c t r i c i a n s o r i g i n a l l y involved in its instal la t i o n . A l l equipment was c a l i b r a t e d individually in t h e laboratory p r i o r ta
i n s t a l l a t i o n t o check accuracy o r determine c a l i b r a t i o n factors. An exception was vane anemometers, which were calibrated a f t e r i n s t a l 1 at i o n
because of t h e dependence
of
a i r flow on actual operating temperature and p r e s s m e . In-situ c a l i b r a t i o n o f t h e vane anemometer was accomplished b ycorrelating
i t s
output ( p l ses/min)
w i t h a d i r e c t flow rate measurementusing a p i t o t tube traverse. A summary of the inst-ruments used, t h e i r
r a n g e , and accuracy i s given in Table 11.
3.3. Comments
'Ika factors common to all t h e demonstration monitoring resulted in
d i s t o r t i o n o r d i s r u p t i o n of the m o n i t o r i n g process. The first was r e l a t e d t o m o n i t o r i n g equipment f a i l u r e and t h e o t h e r t o human e r r o r . Most
equipment failure was associated w i t h the vane anemometers a n d t h e
integrating h e a t meters. The vane anemometers suffered from bearing
failures a f t e r a relatively s h o r t operating period (the brass b u s h i n g s
fai Zed a f t e r one o r t w o months o f operation), and this l e d to e r r o n e o u s
air flow {and hence heat flow) readings.
Malfunction o f the i n t e g r a t i n g h e a t meters ranged f r o m a drift f r o m c a l i b r a t i o n c o n d i t i o n t o complete failure. Failure rate o f the vane
anemometers was as high as 5 0 per cent; for t h e heat meters it w a s 20 per cent. O t h e r factors t h a t disrupted t h e m o n i t o r i n g process were r e l a t e d to the s o l a r system i t s e l f (1). Another source o f error was t h e i n a b i l i t y of some monitoring agents to read meters c o r r e c t l y (such as the d i a l readouts of kwh and gas meters]. This i n d i c a t e d t h e need far well prepared data s h e e t s to minimize m y p o s s i b i l i t y of e r r o r in r e c o r d i n g
d i a l readings and l o c a t i n g decimal p o i n t s .
As a r e s u l t of these problems t h e r e is not a complcte set of
monitored data f o r the 1977/78 h e a t i n g season f o r t h e demonstration houses In many instances even the c o l l e c t e d data were so d i s t o r t e d t h a t meaning- f u l conclusions c o u l d n o t b e drawn r e g a r d i n g the performance o f t h e solar
systems. A summary of the thermal performance of a number of t h e
monitored s o l a r systems has been presented in Reference ( I ) . Work is now
under way to r e c t i f y t h e sources o f e r r o r . A new b e a r i n g for the vane anemometers i s b e i n g d e s i g n e d and new i n t e g r a t i n g h e a t meters are b e i n g
tested and calibrated to replace f a u l t y ones. It i s expected t h a t a complete e v a l u a t i o n of the s o l a r systems "eerfomance will be possible
f o l l o w i n g the 1978/79 season.
4 . MONITORING OF
AYLMER SENIOR
CITIZENS APARTMENT BUILDING SOLAR SYSTEM A senior c i t i z e n s residence located in Aylmer, O n t a r i o , i n c o r p o r a t e sa solar h e a t i n g s y s t e m w i t h a seasonal s t o r a g e u n i t and 219 m2 of l i q u i d - h e a t i n g c o l l e c t o r s . A m o n i t o r i n g system of Level 2Cb) category, w i t h a
minicomputer-based d a t a a c q u i s i t i o n sys tern,
is
being i n s t a l l e d b y NRC,It is based on a D i g i t a l Equipment Corporation E I - 1 1 minicomputer w i d 1
2 8 K memory equipped
with
a dual floppy d i s k unit (250 K) and a Texas I n s trurnen ts model 700 keyboard p r i n t e r . Analogue channels a r einput
through a FIonitor Labs reed scanner and a Fluke 8500 multimeter w i t h binary o u t p u t . Period, rate and l o g i c channels are connected to theLSI-I2 t h m u g h an ADAC o p t i c a l i s o l a t o r i n t e r f a c e ,
F o r each of the 200 channels the system calculates a running
i n t e g r a l based an 30-sec scans. A t each scan t h e measured value is compared w i t h its previous value; if these differ by more than a p r e s e t amount and
if
a p r e s e t "'minimum timet' has elapsed, a new b l o c k of d a t aconsisting of all t h e channels i d e n t i f i e d a s "quickly varyingn i s w r i t t e n
on the f l o p p y d i s k . Data f r o m "slowly varying" channels are written on
the disk a t p r e - s p e c i f i e d t i m e i n t e r v a l s . On-line f ortran routines wi 11 perform running integrations of key performance measurements and d r i v e a
d i s p l a y panel to b e located in the lobby of the b u i l d i n g .
Liquid f l o w and e l e c t r i c a l energy sensors are essentially the same as those described earlier. The kWh meters are equipped w i t h a photo-
e l e c t r i c pulse generator to interface w i t h the minicomputer. Yellow
S p r i n g s Instrument Company precision thermistors matched to w i t h i n
k0.1 C Beg
are
used far temperature measurement, and a #eathertronics t h i n - f i l m capacitive sensor is used to measure r e l a t i v e humidity. S o l a r r a d i a t i o nis
measured w i t h an Eppley 848 pyranometer. A Weathertronicsthree-cup anemometer w i t h a d-c g e n e r a t o r and a vane w i t h a potentiometer
w i l l be used to measure wind speed and d i r e c t i o n , r e s p e c t i v e l y . Air f l o w in the mechanical v e n t i l a t i o n system will b e determined w i t h Validyne p r e s s u r e t r a n s d u c e r s measuring t h e pressure drop across a heat wheel a n d the pressure differentials from averaging p i t o t t u b e s . For comparison, a i r flow will a l s o b e measured with a vane anemometer w i t h a p u l s e d o u t p u t .
Some features are included i n t h i s monitoring system that were not
included in previous systems of the same l e v e l : an automatic power-failure r e s t a r t system, and a d a t a reduction program to a n a l y s e recorded data a s they become a v a i l a b l e . The m o n i t o r i n g system is expected t o b e
operational early in 1979.
5, CONCLUSIONS
- Monitoring systems have been i n s t a l l e d b y NRC in several solar h e a t e d b u i l d i n g s representing a variety o f s o l a r system d e s i g n s
and applications.
- The l e v e l o f the monitoring system installed i n each b u i l d i n g
depended on the t y p e o f b u i l d i n g , the solar system, and the end use of t h e monitoring data produced. Monitoring ranged from
measurement o f conventional fuel consumption o n l y to use o f minicomputer data acquisition systems.
- Valuable experience was gained in designing, calibrating and
instaZling monitoring equipment in various buildings. Ebre effort i s needed in t h e development o r improvement of some of the
measuring equipment, f o r example, t h e vane anemometer and t h e
i n t e g r a t i n g heat metes.
- Cooperation of the m o n i t o r i n g agent and h i s f u l l u n d e r s t a n d i n g a f
t h e solar system and t h e monitoring system operation are v i t a l
factors in c o l l e c t i n g r e l i a b l e d a t a .
REFERENCES
1 . CarscabZen, W.E. and B.E. Sibhitt. S u m a r y o f t h e 197611977 S o l a r
Demonstration Houses. P r e s e n t e d at 1978 SESCI Conference
rRenewable Alternatives,
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