A variety of experiments and simulations, currently being designed or underway, to determine the feasibility of conditioning the source air of an air to air heat pump using stored ground heat or cool to produce higher seasonal COP's and net energy savings are discussed. The ground would condition ambient air as it is drawn through the crawl space of a house. Tests designed to evaluate the feasibility of the concept, to determine the amount of heat or cool available from the ground, to study the effect of the system on the heating and cooling loads of the house, to study possible mechanisms which could enhance heat flow through the ground, and to determine if diurnal temperature swings are necessary to achieve successful system performance are described

Ternes, M. P.

English

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CRAWL SPACE ASSISTED HEAT PUMP 
Mark P. Ternes 
Oak Ridge Nat ional  Laboratory 
PROJECT OUTLINE 
P r o j e c t  T i t l e :  Technology Development o f  Ear th  Storage 
P r i n c i p a l  I nves t i ga to r :  M. P. Ternes 
Organizat ion: Oak Ridge Nat iona l  Laboratory 
P. 0. Box Y 
Oak Ridge, TN 37830 
Telephone: (61 5)  574-0749 
P r o j e c t  Goal s: Develop technology and demonstrate systems f o r  u t i l i z i n g  
heat s to red  i n  undisturbed ea r th  f o r  improving t h e  
performance o f  heat pumps. 
Car ry  ou t  1 aboratory-scale experiments t o  measure the  
apparent thermal c o n d u c t i v i t y  o f  undisturbed ear th  under 
unsteady s t a t e  cond i t ions  and a t  h igh  moisture contents. 
Construct and operate f i e l d  experiments t o  determi ne heat 
t r a n s f e r  and recovery capac i ty  o f  undisturbed e a r t h  under 
r e s i  dent i  a1 b u i l d i n g s  (crawl  space) and i t s  e f f e c t  on t h e  
performance o f  heat pumps f o r  both heat ing  and cool ing.  
P r o j e c t  Status: Laboratory-scale experiment i n  operat ion. F i e l d  study i n  a 
r e s i  den t i  a l  crawlspace was i n i t i a t e d .  
Contract  Number: W-7405-eng-26 
Contract  Period: January, 1979 t o  October, 1980 
Funding Level : $5,000 
Funding Source: U.S. Department o f  Energy 
D i v i s i o n  o f  Energy Storage Systems 
https://ntrs.nasa.gov/search.jsp?R=19800014325 2020-03-21T18:14:09+00:00Z
CRAWL SPACE ASSISTED HEAT PUMP* 
Mark P. Ternes 
Oak Ridge National  Laboratory 
Oak Ridge, Tennessee 37830 
SUMMARY 
A v a r i e t y  of experiments and s imula t ions  a r e  c u r r e n t l y  be ing  designed o r  
a r e  underway t o  determine t h e  f e a s i b i l i t y  of condi t ion ing  t h e  sou rce  a i r  of an 
a i r - t o - a i r  h e a t  pump us ing  s t o r e d  ground hea t  o r  "cool" t o  produce h ighe r  
seasonal  COP'S and n e t  energy savings .  The ground would cond i t i on  ambient a i r  
as it is drawn through t h e  crawl space  of a house. T e s t s  have been designed 
t o  eva lua t e  t h e  f e a s i b i l i t y  of t h e  concept,  t o  determine t h e  amount of h e a t  o r  
I I cool" a v a i l a b l e  from t h e  ground, t o  s tudy  the  e f f e c t  of t h e  system on t h e  
hea t ing  and cool ing  loads  of t h e  house, t o  s tudy p o s s i b l e  mechanisms which 
could enhance h e a t  flow through t h e  ground, and t o  determine i f  d i u r n a l  temp- 
e r a t u r e  swings a r e  necessary t o  achieve  succes s fu l  system performance. A l l  
s t u d i e s  a r e  c u r r e n t l y  ope ra t ing  o r  w i l l  be  o p e r a t i o n a l  by t h e  end of 1979. 
DESCRIPTION 
Higher seasonal  COPfs and ou tpu t  capac i ty ,  accompanied by l a r g e  energy 
savings ,  can p o t e n t i a l l y  be r e a l i z e d  by condi t ion ing  t h e  o u t s i d e  a i r  de l ive red  
t o  an  a i r - t o - a i r  h e a t  pump. The concept t o  be considered i s  a crawl space 
a s s i s t e d  h e a t  pump where t h e  a i r  is  condit ioned by s t o r e d  e a r t h  h e a t  o r  "cool" 
a s  i t  is  drawn through t h e  crawl space of a house. A schematic  r e p r e s e n t a t i o n  
of t h i s  concept is shown i n  F ig .  1. 
I n  1977, a graduate  s tuden t  a t  The Univers i ty  of Tennessee conducted a 
f i e l d  experiment a t  a p r i v a t e  res idence  i n  Oak Ridge, Tennessee, wi th  t h e  
h e a t  pump ope ra t ing  i n  t h e  above mode dur ing  t h e  win te r  season  and observed 
*Research sponsored by t h e  Div is ion  of Energy Storage  Systems, U.S. 
Department of Energy under c o n t r a c t  W-7405-eng-26 wi th  t h e  Union Carbide 
Corporation. 
By acceptance of t h i s  a r t i c l e ,  t h e  pub l i she r  o r  r e c i p i e n t  acknowledges 
t h e  U.S. Government's r i g h t  t o  r e t a i n  a nonexclusive, roya l ty - f r ee  l i c e n s e  
i n  and t o  any copyright  covering t h e  a r t i c l e .  
t h a t  s i g n i f i c a n t  i nc reases  i n  a i r  temperature were, i n  f a c t ,  achieved. A 
number of ques t ions  remained which need t o  be  answered, however, be fo re  t h e  
f e a s i b i l i t y  and gene ra l  a p p l i c a b i l i t y  of t h e  concept can be  assured;  i t  is  
unresolved whether t h e  temperature i n c r e a s e  of t h e  a ir  was due t o  h e a t  addi- 
t i o n  from the  ground o r ,  r a t h e r ,  due t o  conduction and/or  a i r  e x f i l t r a t i o n  
through t h e  f l o o r  of t h e  house, and thus  t h e  p o s s i b l e  e f f e c t s  of t h e  system 
on t h e  hea t ing  and cool ing  loads  of t h e  house are unknown. It i s  a l s o  uncer- 
t a i n  what t r a d e o f f s  were involved i f  t h e  t e m p e r a t ~ r ~  change w a s  p a r t i a l l y  due 
t o  house h e a t  l o s s e s  and p a r t i a l l y  due t o  ground h e a t  add i t i on .  I f  t h e  e a r t h  
i n  an enclosed space can, indeed, supply a s i g n i f i c a n t  quan t i t y  of  h e a t  t o  a i r  
flowing above i t ,  then  f u r t h e r  s t u d i e s  of t h e  h e a t  t r a n s f e r  and s t o r a g e  char- 
a c t e r i s t i c s  of t h e  e a r t h  become of  i n t e r e s t ;  namely, whether t he  r equ i r ed  h e a t  
f l u x  through t h e  s o i l  and t o  t h e  a i r  is exp la inab le  by s imple conduction and 
convection of e a r t h  h e a t ,  whether t h e  h e a t  flow r a t e  through s o i l  can be en- 
hanced by moisture d i f f u s i o n  induced by temperature g rad ien t s ,  and whether 
d i u r n a l  temperature swings e f f e c t i v e l y  "charge" t h e  upper-most l a y e r  of t h e  
e a r t h  during t h e  daytime. Three s e p a r a t e  a r e a s  of i n v e s t i g a t i o n  a r e  underway 
t o  address  t h e s e  ques t ions .  
The f i r s t  i n v e s t i g a t i o n  c o n s i s t s  of a f i e l d  t e s t  of a second house mod- 
i f i e d  such t h a t  ambient a i r  i s  drawn through t h e  crawl space and de l ive red  t o  
t h e  h e a t  pump. It i s  s i m i l a r  t o  the  i n i t i a l  f i e l d  t e s t  except  t h a t  a d d i t i o n a l  
ins t rumenta t ion  is be ing  u t i l i z e d .  The o b j e c t i v e  of t h i s  second f i e l d  t e s t  is  
t o  r ea f f i rm  t h e  f e a s i b i l i t y  of t he  concept a s  w e l l  a s  t o  record and understand 
the  t r a n s i e n t  c h a r a c t e r i s t i c s  and responses of t he  crawl space. A p l a s t i c  
moisture b a r r i e r  w i l l  cover t he  e a r t h  s u r f a c e  t o  prevent  moisture evaporat ion.  
Crawl space a i r  temperatures ,  ground s u r f a c e  temperatures ,  and e a r t h  tempera- 
t u r e s  0.15 m (6  i n . )  below t h e  s u r f a c e  w i l l  b e  cont inuously recorded us ing  a 
12-point Honeywell r eco rde r  and type K thermocouples. An event  r eco rde r  w i l l  
a l s o  be  used t o  monitor t h e  d e f r o s t  cyc l e s  of t h e  h e a t  pump. Figure 2 shows 
a schematic of t h e  crawl space and t h e  thermocouple l oca t ions .  
The second i n v e s t i g a t i o n  w i l l  c o n s i s t  of measuring the  temperature r i s e  
of ambient a i r  drawn by po r t ab l e  f ans  through two s p e c i a l l y  b u i l t  i n s u l a t e d  
duc ts  l oca t ed  i n  t h e  crawl space of an experimental  c o n t r o l  house being used 
i n  conjunct ion wi th  energy conserva t ion  p r o j e c t s  a t  ORNL. A plan  view is  
shown i n  Fig. 3. Three s i d e s  of t h e  duc t  w i l l  be  formed of c losed c e l l  poly- 
s t y r e n e  shee t ing  0.30 m (12 i n . )  t h i c k ,  w i th  t h e  remaining s i d e  being open t o  
t he  ground. The f a n  w i l l  be  cycled through d i f f e r e n t  "on/offW sequences wi th  
the  use  of a 24-hr t imer  t o  s imula te  a c t u a l  h e a t  pump opera t ion .  Two duc t s  
w i l l  be  used - one w i t h  a p l a s t i c  moisture b a r r i e r  on t h e  e a r t h  s u r f a c e  and 
t h e  o t h e r  wi thout  - t o  ga in  a q u a n t i t a t i v e  understanding of t h e  d i f f e r e n t  h e a t  
t r a n s f e r  mechanisms occu r r ing  i n  s o i l .  With a l l  j o i n t s  i n  t h e  duc ts  c a r e f u l l y  
s ea l ed ,  t he  duc t s  w i l l  be  thermally i s o l a t e d  from t h e  house a s  w e l l  a s  t h e  
crawl space,  and thus  any temperature r i s e  r e s u l t i n g  from a i r  flowing through 
t h e  duc ts  w i l l  b e  due s o l e l y  t o  hea t  a d d i t i o n  from t h e  ground. It w i l l ,  
t he re fo re ,  be  p o s s i b l e  t o  determine d i r e c t l y  t h e  amount of u s e f u l  h e a t  a v a i l -  
a b l e  from t h e  ground and, from comparisons wi th  f i e l d  experiments,  it w i l l  b e  
p o s s i b l e  t o  determine t h e  sou rce ( s )  of t h e  h e a t  ga ins  experienced i n  a c t u a l  
f i e l d  opera t ion .  Moreover, ques t ions  concerning t h e  n e c e s s i t y  of d i u r n a l  
temperature swings and t h e  impact of t h e  system on t h e  house environment w i l l  
bo th  b e  p a r t i a l l y  addressed.  Duct temperatures ,  ground s u r f a c e  temperatures,  
and e a r t h  temperatures  0.15 m ( 6  i n . )  deep w i l l  be  cont inuously recorded us ing  
a 12-point Honeywell r eco rde r  and type  T thermocouples; a d d i t i o n a l l y ,  a i r  
v e l o c i t y ,  wet-bulb temperatures ,  and s o i l  moisture con ten t  w i l l  be  measured 
p e r i o d i c a l l y .  
The t h i r d  i n v e s t i g a t i o n  w i l l  address  two i s s u e s  p a r t i a l l y  addressed 
beforehand: s p e c i f i c a l l y ,  t h e  e f f e c t . o f  d i u r n a l  temperature swings on t h e  
thermal  condi t ions  of t h e  ground and t h e  e f f e c t  of mois ture  d i f f u s i o n  on t h e  
h e a t  t r a n s f e r  c h a r a c t e r i s t i c s  of s o i l .  Mathematical and computer modeling 
techniques a r e  be ing  employed t o  determine t h e  s t o r a g e  and recovery capabi l-  
i t i e s  of t h e  e a r t h  when exposed t o  c y c l i c  temperatures  and t o  eva lua t e  t h e  
e f f e c t i v e n e s s  and importance of t h e  temperature swings i n  charging the  e a r t h  
system dur ing  t h e  daytime. The enhancement of s o i l  h e a t  t r a n s f e r  is  be ing  
s t u d i e d  i n  a 0.61 m (2  f t )  square  box 0.30 m ( 1  f t )  h igh ,  capable of maintain- 
i n g  a cons tan t  f r e e  s u r f a c e  water  l e v e l  i n  t h e  s o i l  t e s t  s e c t i o n  and an i m -  
posed h e a t  f l u x  through the  bottom. Temperatures a r e  measured throughout t he  
box us ing  type K thermocouples and t h r e e  Honeywell r eco rde r s ;  moisture content  
i s  monitored us ing  f i b e r  g l a s s  encased moisture probes.  A schematic of t he  
t e s t i n g  device  i s  shown i n  Fig.  4. 
STATUS 
The h e a t  pump modif ica t ions  have been made f o r  t h e  second f i e l d  t e s t ,  and 
d a t a  a c q u i s i t i o n  has begun. Prel iminary r e s u l t s  show t h a t  f o r  ambient a i r  a t  
O°C (32OF) and ground s u r f a c e  temperatures  of 10.6OC (51°F),  a i r  was de l ive red  
t o  t h e  h e a t  pump a t  5.0°C (41°F). Acquis i t ion  of m a t e r i a l s  and instrumenta- 
t i o n  f o r  t h e  duc t  experiment i s  underway, and i t  is expected t h a t  t he  duc ts  
w i l l  be  cons t ruc ted  and o p e r a t i o n a l  by t h e  end of 1979. To d a t e ,  t h e  e f f e c t i v e  
thermal conduct iv i ty  of wet c l a y  as measured i n  t he  thermal  conduct iv i ty  ex- 
periment has  been found t o  be  1 .21  W/m O C  (0.7 Bt?u/h f t  OF) which conforms 
wi th  l i t e r a t u r e  va lues ,  and thus  no s i g n i f i c a n t  h e a t  t r a n s f e r  enhancement has  
been found. 
F i g .  1. Crawl  Space A s s i s t e d  H e a t  Pump 
TEMPERATURE 
MEASUREMENTS 
AIR TEMPERATURE 
SURFACE TEMPERATURE 
Gin.-DEEP EARTH 
TEMPERATURE 
DISCHARGE 
F i g .  2. F i e l d  T e s t  C o n f i g u r a t i o n  
TEMPERATURE 
MEASUREMENTS 
x AIR TEMPERATURE 
o SURFACE TEMPERATURE 
6-in.-DEEP EARTH 
TEMPERATURE 
Fig. 3.  Plan View of the Duct Experiment 
WATER 
SUPPLY 
HEAT INPUT USING RESISTANCE ELEMENTS 
Fig. 4. Thermal Conductivity Testing Device 
276 


Crawl space assisted heat pump

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