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ENERGY CONSERVATION EXPERIENCES VITH HV C SYSTEMS I N THE H I G H HUMIDITY CLIMATE.

CASE HISTORY

Tom R Todd

P r i n c i p a 1

E n g i n e e r i n g S c i e n c e s , I n c .

Memphis, T enn ess ee 38112

The pu r po s e of t h i s p a p e r i s t o d i s c u s s s e v -

e ra 1 commonly en co u n te red p ro b lems ass o c i a te d wi th

a t t e m p t s t o a i r c o n d i t i o n b u i l d i n g s i n t h e humid

environment. I t f i r s t , r e p o r t s o b s e rv a t i o ns made

i n t h e co u r s e o f s t u d y i n g t h e a i r c o n d i t i o n i n g

s y s t er ns i n a p p r o x i m a t e l y o ne h u n dr ed b u i l d i n g s a t

USMC Camp Smedl ey D B u t le r in Ok in awa, Jap a n .

Three common problems a r e then d isc uss ed i n some

d e t a i l .

I t was found t ha t i n many case s humidity con-

s i d e r a t i o n s l e a d t o s i t u a t i o n s w h ic h w er e e ne r g y

w a s t e f u l . I n many i n s t a n c e s t h i s c ou ld b e a t t r i -

b u te d t o e i t h e r d e s i g n o r o p e r a t i o n a l e r r o r s . The

most common e rr o r found was the s el ec t io n of an

improper method of ca pa ci ty con tr o l . Methods of

i mp ro ve d c a p a c i t y c o n t r o l a r e s u g g e s t e d an d t h e

n ee d f o r a d d i t i o n a l work i s p o i n t e d o u t .

INTRODUCTION

During th e summers o f 1983 and 1984 Engi-

n e e r i n g S c i e n c e s , I n c. p e r s o n n e l p e r fo r me d f i e l d

s u r v e y s of a p p r o x i m a t e l y o ne h un dr e d b u i l d i n g s a t

USMC Camp Sme dle y

D

B u t l e r i n O k in aw a, J a p a n

u nd er a c o n t r a c t w i t h t h e P a c i f i c D i v i s i on o f t h e

Nava l Fa c i l i t i e s En g in ee r in g Command. The p urp o se

of t h i s c o n t r a c t was t o i d e n t i f y d e f i c i e n c i e s i n

t he a i r c o n di t i o n in g e qu ip m en t w hi ch a f f e c t s i t s

e n er g y co ns um p ti o n an d i t s a b i l i t y t o p r ov i de t h e

r e q u i r e d s p a c e c o n d i t i o n s .

The f i r s t s t e p i n t h i s p r o c e s s was t o p e rf o rm

a r a t h e r e x t e n s i ve f i e l d t e s t o f t h e a i r c on di -

t i o n i n g eq u ip m e nt a nd i t s c o n t r o l s . The ESI f i e l d

s u rv e y t eam m e as ur ed a l l p e r t i n e n t o p e r a t i n g v a r i -

a b l e s (e.g., a i r fl o w s , d r y a n d w e t b u l b a i r t em -

p e r a t ur e s , a i r s t a t i c p r e s s u r e s , w a t e r f l ow s ,

wa t e r / r e f r i g e r a n t t e m p e r a t u r e s , w a t e r p r e s s u r e

d ro ps , a l l a p p ro p r i a t e mo to r e l e c t r i c a l d a t a ,

etc.).

A l l

c o n t r o l e q u i p m en t wa s e x e r c i s e d o v e r

i t s e n t i r e r a n g e of m o t io n an d r e a d in g s r e t a k e n

f o r a l l v a r i a b l e s . I n a d d i t i o n d r y a nd w e t b u l b

a i r t e m p e r a t u r e s w e r e t a k e n t h ro u g h o ut t h e c on -

d i t i o n e d s p a c e s and a t h or o ug h v i s u a l i n s p e c t i o n

made of th e eq u ip men t an d th e sp aces th a t

i t

s er ve d. More s p e c i f i c a l l y , s u f f i c i e n t e n g i n ee r -

i n g d a t a was c o l l e c t e d t o a l l o w t he c a l c u l a t i o n

of t h e r m a l l o a d s f o r t h e b u i l d i n g s .

U si ng t h e d a t a c o l l e c t e d t h e o p e r a t i n g p o i n t

fo r each p iece o f eq u ip m en t was id e n t i f ie d an d u sed

t o s p e c i f y t h e o p e r a t i n g p o i n t of t h e e n t i r e a i r

c o n d i t i o n i n g s y s t e m a t t h e t i m e of t h e s u rv e y .

From knowledge of the ambi ent co ndi t i ons and load -

i n g a t t h e t i m e of t h e s u r ve y , i t w as p o s s i b l e t o

p r e d i c t t h e p er f o r m an c e of t h e e q u ip m e nt a t d e s i g n

c o n d i t i o n s a nd a t t h e v a r i o u s p a r t l oa d c o n d i t i o n s

t h a t

i t w i l l

e x p e r i e n c e d u r i n g t h e c o u r s e of a

y ear . (Th is was p o s s ib l e th ro u g h th e u s e o f a

n u mb er o f co mp u ter ro u t in es t h a t ESI h as d ev e lo p ed

f o r t h i s p u r po se .)

H av in g a n a l y z ed t h e s y s t e m s i n t h i s f a s h i o n ,

d e f i c i e n c i e s ( i n d e s i g n a n d / o r c o n d i t i o n ) w hi c h

c a u s e them t o f a i l t o p e rf o rm t h e i r d e s i r e d f u n c -

t i o n i n a n e f f i c i e n t ma nn er c ou l d be i d e n t i f i e d .

R ecommend at io n s were th en mad e to co r r e c t t h es e

p r o b l em s an d s u p p o r t i n g c a l c u l a t i o n s p er f o r m ed t o

a s s e s s t h e e co no mi c a t t r a c t i v e n e s s of e a c h i n v e s t -

men t

As ex p ec t ed , many o f t h e p ro b lems o b serv ed in

t h e c o u r s e of t h e wo rk w e r e hu m i d i t y r e l a t e d . T h i s

i s c o n s i s t e n t w i t h t h e f a c t t h a t Okin aw a i s a v e ry

h umid en v i ro n men t . Amb ien t d es ig n co n d i t io n s (2.5

) a r e 8 8 / 8 0

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co nd en se o n th e d i f fu se r s an d cau se p ro p er ty dam-

a ge . T h i s c o n d i t i o n w as v e r i f i e d by t he f i e l d

team. Again th e r e su l t was th a t sh u td o wn was fo r -

f e i t e d a nd t h e e q u i p m e nt o p e r a t e d c o n t i n u o u s l y

wi th o u t r eg ard to o ccup an cy . As b efo re , th i s

cau sed co n s id e rab le was te o f en ergy .

Th is p ap er w i l l c o n c e n t r a t e e x c l u s i v e l y o n

t h e s e t h r e e i s s ue s . P r i m a ry a t t e n t i o n w i l l be

g i v e n t o t h e pr o bl e m s a s s o c i a t e d w i t h c o n d e ns a t i o n

du ri ng norm al op er at io n (No. 1). No.

2

and No. 3

w i l l be d iscu ss ed in g en era l t e rms an d r ecommend a-

t i o n s m ade. T h i s i s n o t m e a nt t o m i n i m iz e t h e

m y ri a d o f o t h e r h u m i d i t y r e l a t e d i s s u e s w h i ch a f -

f e c t b u il d i n g s i n t h e s e c l i m a t e s. The f i e l d i s

we ll developed and much has been writ te n .

t s h ou l d a l s o be p o i n t e d o u t t h a t t h e r e a r e

a n umber o f d es ig n i s su es wh ich can ten d to in -

c r e a s e t h e s e v e r i t y o f t h e a bo ve t h r e e p r ob l em s .

These w i l l b e m e n ti o ne d o n l y b r i e f l y :

1. C h i l l e d w a t e r t e m p e r a t u r e s a r e f r e q u e n t l y

f ou nd t o b e e l e v a t e d f o r t h e s a k e o f e n e r g y c on -

s e r v a t i o n . I n a d d i t i o n t o b e i ng a po or way o f

s a v i n g e n e rg y , t h i s

w i l l

u s u a ll y r e s u l t i n a l o s s

o f l a t e n t c a p a c i t y an d a l o s s of h u m i d i t y c o n t r o l

i n t h e sp a c e. ( F i g u r e 1 s ho ws t h e e f f e c t of e n -

t e r i n g c h i l l e d w a t e r t e m p e ra t u r e o n t h e s e n s i b l e

a nd l a t e n t c a p a c i t i e s o f a t y p i c a l c o il . ) C h i l l e d

w a t e r t e m p e r a t u r e s i n h um id c l i m a t e s s h o u l d be

k e p t a s l ow a s p o s s i b l e .

2

V e n t i l a t i o n a i r b r ou g ht i n t h ro ug h t h e

a i r ha n dl i n g u n i t i s o f t e n r ed uc e d t o s a v e e ne rg y.

U n f o rt u n a t e ly t h i s i s u s u a l l y d one w i t h ou t a c o r -

r e sp o nd i n g r e d u c t i o n i n e x h a u st a i r . As a r e s u l t

p r e s su r i z at i o n i s l o s t a nd i n f i l t r a t i o n i s i n -

c r e a s e d. I n a h um id c l i m a t e t h i s i s p a r t i c u l a r l y

bad b e ca us e t h e i n f i l t r a t i n g a i r b r in g s a hi g h

m o i s t u re l o ad d i r e c t l y i n t o t h e c on d it i o ne d s p ac e ,

r a i s in g th e room dew p o in t . (F ig u re

2

shows the

change in room co ndi t i on due t o the exchange of

v e n t i l a t i o n a i r f o r a n e q u i v a l e n t a mount of i n f

il

t r a t i o n . )

A l l

s p a c e s s h o u l d be p r e s s u r i z e d w i t h

c o n d i ti o n e d o u t s i d e a i r .

3. M os t o f t h e b u i l d i n g s i n s p e c t e d w e r e v e r y

l oo se a nd e x p e r i en c e d a h i g h r a t e of i n f i l t r a -

t io n . I n so me cas es th ere was ev en a d es ig n ten -

d ency to en co u rag e f r e sh a i r . (F ig u re 3 shows

t h e e q u i l i b r i u m r oom c o n d i t i o n s f o r v a r i o u s

a m ou nt s o f i n f i l t r a t i o n . ) E ve ry e f f o r t s ho u ld b e

made t o make t h e s p a c e s a s t i g h t a s p o s s i b l e t o

m i n im i z e t h e a mo un t of m o i s t u r e b r o ug h t d i r e c t l y

i n t o t h e s p a c e .

4

In many cases i t was fou nd t h a t co o l i n g

c o i l s ha d n o t be en s e l e c t e d w i t h p r o pe r c a r e .

M os t o f t e n t h i s m e an t t h a t t h e c o i l was s e l e c t e d

w i t h o u t c o n s i d e r a t i o n of l i k e l y p a r t l o a d c on d i-

t i o n s . A l l c o i l s s h o ul d b e ch e ck e d f o r p e r f o r -

m anc e u n de r t h e e n t i r e r a n g e o f c o n d i t i o n s t h ey

may be subjected to.

CONDENSATION

ON

DIFFUSERS

D U R I N G

NORMAL OPERATION

Nat ure of the Problem

Probably the most common problem observed in

Okinawa was the condensa tion of mo is tu re on supply

a i r di f f u s e r s . F i gu r e 4 sh ow s a t y p i c a l c e i l i n g

d i f fu se r . C o n d ensa t io n o cc u r s when warm, mo i s t

a i r c om es i n t o c o n t a c t w i t h a s o l i d o b j e c t h a vi ng

a s u r f a c e t e m p e r a t u r e b el o w i t s de w p o i n t .

T h i s c a n o c c ur i n s e v e r a l ways. The f i r s t

p o s s i b l i t y c o n ce r ns m od u l a t i ng t y p e c o n t r o l s y s -

tems.

W i t h t h e s e s y s t e m s o n e d o e s n o t n o r m a l l y

s e e a s ud de n c ha ng e i n t h e c o n d i t i o n o f t h e s u p p l y

a i r b ei ng di sc ha rg ed a t t he d i f f us e r . I n t h l s

c a s e t h e p r i m a r y m ec ha ni sm f o r c o n d e n s a t i o n i s t h e

i n d u c t i o n of r oom a i r . M o i s t room a i r i s i n d uc e d

t o f l o w a l o n g t h e c e i l i n g an d o ve r t h e o u t e r

c a s i n g o f t h e d i f f u s e r . T he c e i l i n g a nd d i f f u s e r

c a s i n g a r e c o o le d by b o t h c o n d u c t i o n a nd t h e e f -

f e c t o f a i r l ea ke d a t t h e c on ne c to r.

A s

o n e m i g h t i m a gi n e , t h i s

i s

a v e r y g e o m e t r y

sp e c i f i c phenomenon.

t

i s a w e l l known f a c t t h a t

i n m o s t c a s e s o ne c a n s u p p l y a i r a t s o me t e m pe r a -

tu re b e lo w th e room dew p o i n t w i th o u t co n d en sa t io n

occ urr i ng . But, to our knowledge, no one has

e x p e ri m e n t a ll y o r a n a l y t i c a l l y q u a n t i f i e d t h e

a l l o w a b l e t e m p e r a t u r e d e p r e s s i o n . ( So me wh er e i n

th e r a n g e o f 5 -OF to ?OF i s g e n e r a l l y f e l t t o b e

accep tab le . Th is h as , in d eed , b een co n f i rmed b y

ESI ' s o b s erv a t io n s in Ok inawa. )

T h e r e do e s se em t o b e a m ar ke d d i f f e r e n c e i n

t h e t e nd e nc y of d i f f e r e n t d i f f u s e r d e s i g ns t o e x-

p e r i e n c e c o n d e n s a t i o n p r o b l em s w hen s u b j e c t e d t o

t h e sa me s u p p l y a i r / d e w p o i n t d e p r e s s i o n . A g a in ,

to o u r k n o wled ge , n o o ne h as su cceed ed e i t h e r ex -

p e r i m e n t a l l y o r a n a l y t i c a l l y i n g i v i n g more t h an

q u a l i t a t i v e g ui de s f o r s e l e c t i o n o f d i f f u s e r s f o r

t h i s t y p e o f s e r v i c e.

t i s

g e n e r a l l y a gr ee d t h a t

t h e s m a l l e r t h e ou t e r c a s i n g ( t o a c t a s a f i n ) a nd

t h e l o w er t h e a i r v e l o c i t y ( t o i nd uc e a room a i r

f l o w ) t h e b e t t e r . Some h av e s u g g es t e d t h a t p l a s t i c

d i f f u s er s wo uld be wo rse co n d u c to r s an d , h en ce ,

b e t t e r . The v a l i d i t y o f t h e o u t e r c a s i n g f a c t o r

was v e r i f i ed b y th e f i e l d work in Ok in awa. The

ty p es o f d i f f u s er s wh ich seemed t o be mo s t su scep -

t i b l e t o t h i s p ro bl em h ad l a r g e m e t a l o u t e r r i n g s

surrounding them.

In many cas es where proble ms were observed

t h e c a u s e wa s fo un d t o be a i r l e a k s i n t h e f l e x i -

b l e c o nn e ct o r. T h is se em s t o b e o f c r i t i c a l i m

p o r t a n c e i n t h e s e c l i m a t e s . ( Th e s e p a r a t e , b u t

r e l a t e d p r ob le m , o f m o i s t u r e c o nd e n s a t io n i n s i d e

d u c t i n s u l a t i o n wa s a l s o c om mo nl y fo u nd a nd f r e -

q u e n t l y a s s o c i a t e d w i t h a i r l e a ka g e. )

Method of Capa cit y Con tro l

By f a r t h e m os t i m p o r t a n t f a c t o r i n f l u e n c i n g

th e fo rm at i o n o f co n d en sa t io n was fou n d to b e th e

meth od o f cap ac i ty co n t ro l emp loy ed . One co n t ro l

wh ich was f r e q u en t ly fo u n d o n sm al le r

DX s y s t e m s

wa s t o c l o s e a r e f r i g e r a n t s o l e n o i d i n r e s p on s e

t o s a t i s f a c t i o n o f a room o r r e t u r n a i r t h e r m os t a t.

ESL-HH-85-09-05

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G e n er a l ly t h e a i r h a n dl i n g u n i t f a n w as a l l o w e d

to run cont inuou sly. Much has been wr i t te n of th e

e f f e c t s o f r e e va p o r a t i o n o n room h u m i d i ty r a t i o

i n c o n t r o l s y s t e m s o f t h i s ty p e ( 1) . An a d d i -

t i on a l p rob lem can be s een when one cons ide rs th a t

t h e a i r h a n d l i n g u n i t b e g i n s t o s en d a n un co nd i-

t i o n ed m i x t u r e o f r e t u r n e d room a i r a nd o u t s i d e

v e n t i l a t i o n a i r t h ro ug h d u c t s a nd a c r o s s d i f f u s e r s

which were, moments bef or e , cooled by cold sup ply

a i r . O b s er v a ti o n s o f c e i l i n g s t a i n s and r u s t e d

d i f f u s e r s r e i n f o r c e d t h e c a s e s w h er e a c t u a l co n-

dens a t ion forma t ion of th i s type was obse rved .

S p e i l v o g e l c o n f i r m s t h e s e o b s e r v a t i o n s i n an

ea r l i e r s tudy a l s o pe r formed f or the Navy (2).

The impac t of the me thod of capac i ty con t r o l

on condensa t ion i s somewhat more su bt le f o r modu-

l a t i n g t y pe s of c o n t r o l . I t c a n b e r e du c ed t o t h e

fol low ing two issue s : 1) How we l l i s the room

humidi ty cont r o l l ed ? 2) How does supply a i r d ry

b u l b t e m p er a t ur e v ar y w i t h l o a d ? The f i r s t i s s u e

w i l l

d i c t a t e t h e room a i r ' s d ew p o i n t an d t h e

s e co n d d e t e r m i n e s t h e t e m p e r a t u r e d e p r e s s i o n a s a

func t ion of load .

A l l methods of modula t ing capac i t y co nt ro l

c a n b e t ho u g h t o f a s v a r i a t i o n s o f t w o b a s i c

methods . The f i r s t i s t o d e c r e a s e t h e a m ou nt

o f w a t e r a l l o w e d t o f l ow t h ro u g h t h e c o i l . T h i s

c a u se s t h e e f f e c t i v e t e m p e ra t u re o f t h e c o i l t o

r i s e an d h e nc e l e s s h e a t t r a n s f e r oc c u rs . The

s ec on d i s t o d e c r e a s e t h e am o un t o f a i r f l o w i n g

t h ro u gh t h e c o i l . T h i s a l s o r ed u c e s t h e a m ou n t

o f h e a t t r a n s f e r . ( A c t u a l l y t h e r e i s a t h i r d

p o s s i b i l i t y . One c o u ld v a r y t h e t e m p e ra t u r e o f

t h e wa t e r e n t e r i n g t h e c o i l b u t , a s h a s a l r e a d y

been shorn , t h i s has und es i rh b le consequences and

i s n o t g e n e r a l l y f o u n d . )

Before d i s cus s in g each of these , some cons i -

d e r a t i o n s h o u ld b e g i v e n t o l i k e l y p a r t l o a d c on -

d i t i o n s . I t h a s be en g e n e r a l l y f ou nd t h a t t h e

c o i l s e n s i b l e h e a t r a t i o r e q u i r e d f o r mo st common

p a r t l o a d c o n d i t i o n s

i s

l o w e r t h a n t h a t r e q u i r e d

a t d e s i g n c o n d i t i o n s . T h i s te n de n cy is p a r t i c u -

l a r ly t ru e in humid c l im a t es such as Okinawa.

Consider a ca se which was found to be problem

p ro ne . Mess h a l l s t y p i c a l l y h av e l a r g e i n t e r n a l

loads due to people and food s e rv ice . Suppose

t h a t a n a i r c o n d i t i o n i n g s y s t e m ha s be en d e s ig n e d

t o s a t i s f y t h e l o ad when t h e a m b i e n t

i s

88/80

i°F/OF).

T h e r e w i l l o f c o u r s e , b e a s o l a r l o a d

i n c lu d e d i n t h e d e s i g n c a l c u l a t i o n s .

A

p a r t l o a d

c o n d i t i o n f r e q u e n t l y e n c o u n t e r e d i s t h a t o f a

ra i ny day dur i ng the des ign month . Obse rva t ion

h a s sh own t h a t t h e a m b i e n t h u m id i t y r a t i o r e m a i n s

re l a t i ve ly cons t e n t th roughout any g iven day . (The

r e l a t i v e h u m i d i t y i s i n v e r s e l y r e l a t e d t o t h e d r y

bulb temperature .) On a ra in y day the amb ien t

dry bu lb m ight go t o 80-OF but the we t bu lb might

w e l l b e a s h i g h a s 78-OF. T he l a t e n t l o a d d u e t o

v e n t i l a t i o n a nd i n f i l t r a t i o n a i r i s u nchanged b u t

the s e ns ib le load has been reduced 80 . The so la r

l o a d ( a l l s e n s i b l e ) i s re d u c ed t o z er o. T he i n -

t e r n a l p e o p l e a n d fo o d s e r v i c e l o ad i s unchanged.

The n e t r e s u l t of a l l of t h i s i s t h a t t h e s en s i b l e

h e a t r a t i o r e q u ir e d o f t h e c o i l i s d im i n is h e d

s u b s t a n t i a l l y . T h is i s a d m i t t e d l y , a n e x t r e m e

c a s e b u t t h e s am e g e n e r a l t e nd e nc y i s s e e n i n a

v a r i e t y o f b u i l d i n g t y p es .

A computer program ha s been developed wh ich

i s u s e f u l i n p r e d i c t i n g t h e p er f or m an c e o f a g i v e n

c o i l u n d er v a r i o u s l o a di n g c o n d i t i o n s . T h i s p r o -

gram i s based upon pr i nc ip le s de sc r ib ed by Nuss -

baum b ut uses known pe r formance a t one s e t o f

c o n d i t i o n s t o d e t er m i n e e m p i r i c a l l y t h o s e c on -

s t a n t s w h i ch d e t e r m i n e i t s p er fo rm an ce a t o t h e r

c o n d i t i o n s (3). I n t h i s m an ne r on e c a n i n p u t o n e

known oper a t i ng po in t and pr ed ic t how the co i l

w i l l

b eh av e u n d er a n y o t h e r s e t o f c i r c u m s t a n ce s .

Thi s p rogram has been used ex t ens ive ly in th e

f 01 owing manner.

F i g u r e

5

shows the pe r formance of a ty p i ca l

c h i l l e d w a t e r c o i l t h ro u gh wh ic h t h e wa t e r f l o w i s

v a r i e d . The p l o t s ho ws t h a t t h e l a t e n t c a p a c i t y

f a l l s o f f m uch f a s t e r t h an t h e s e n s i b l e c a p a c it y .

T h i s i s j u s t t h e o p p o s i t e of w h at i s d e s i r e d a n d

t h e r e s u l t w i l l be th a t t he room hu midi ty and dew

p o i n t w i l l i n c r e a s e a t p a r t l o ad c o n d i t i o n s . T h e

t e m p e r a t u re o f t h e s u p pl y a i r i n c r e a s e s a s t h e

c a p a c i t y d ec r e as e s. T h i s i s a v e r y d e s i r a b l e

c h a r a c t e r i s t i c i n t r y i n g t o a v o id c on de ns at io n.

F i g u r e p r e s e n t s t h e s am e i n f o r m a t i o n f o r

t h e c a s e wh er e t h e a i r f l ow i s va r i ed . The c o i l

i s u n c o nt r o l l e d i n t h i s ca se . One c an s e e t h a t

t h e s e n s i b l e c a p ac i ty f a l l s f a s t e r t ha n t h e l a t e n t

r e s u l t i n g i n a l o we r s en s i b l e h e a t r a t i o a t p a r t

l o a d s. T h i s i s a s - o n e w ou ld w an t. B u t n o t i c e

t h a t t h e s up p l y a i r t e m pe r at u re f a l l s v e ry r a p i d l y

a s t h e l o a d i s d e c re a s ed . I f t h e room dew p o i n t

we re t o r em a in r e l a t i v e l y c o n s t a n t a t

63 OF (78-OF

w i t h r e l a t i v e h u mi d it y o f

60

a s Navy d e s i g n c r i -

t e r i a r e q u i r e s ) t h e d e p r e s s io n of t h e t e m p e r a t ur e

o f t h e s u p p l y a i r b el ow d ew p o i n t w ou ld i n c r e a s e

ra p i d l y and con densa t ion would be exper i enced .

(One m i gh t a t t e m p t t o s o l v e t h i s d e f i c i e n c y b y

co n t r o l l i n g t h e s u p p l y a i r d i s c h a r ge t e m p e r a t u re

w i t h a v a l v e on t h e c h i l l e d w a t er l i n e b u t

i t

can

b e sh ow n t h a t t h i s i m m e d i a t el y b e g i n s t o d i s p l a y

t h e s e n s i b l e h e a t r a t i o i n c r e a s e f ou nd w i t h t h e

ch i l l e d w a te r va lve method d i s cus sed above .)

F i g u r e

7

shows what i s commonly re fe r r ed t o

a s f a c e a n d b y p a ss c o n t r o l . T h i s i s , h o we v er ,

n o t h i n g m or e t ha n v a r i a b l e a i r f l o w t h r o ug h t h e

c o i l i n w hi ch t h e a i r n o t pu t t h ro ug h t h e c o i l i s

bypas sed and mixed back wi t h t ha t which has been

c o o le d an d d eh u mi d if i ed . I n f a c t , t h e h e a t t r a n s -

f e r i s e x a c t l y t h e sa me a s t h e c a s e d i sc u s s e d f o r

v a r i a b l e a i r f lo w. The s e n s i b l e h e a t r a t i o f a l l s

in the s ame way t ha t i t d i d ( a n d a s i s des i red) .

The s u p p l y a i r t e m p e r a t u r e , h ow ev er , r i s e s q u i c k l y

a s t h e l o a d i s reduced . Thi s so lv es the problem

o f i n c r e a s i n g d e p r e s s i o n a nd a v o i d s t h e p o t e n t i a l

f o r c o n d e n s a t i o n p r ob l em s f o un d w i t h t h e v a r i a b l e

a i r f l o w s y st em .

As c a n be s e e n t h e s u p p l y a i r t e m p e r a t u r e f o r

t h e f a c e a n d b y pa s s s y st e m r i s e s much f a s t e r t h a n

i s

n e c es s a ry . T h i s s u g g e s t s t h e p o s s i b i l i t y of

c o mb i ni n g t h e f a c e a nd b yp a s s w i t h t h e v a r i a b l e

a i r vo lume sys tem (F igure 8) . The fan speed might

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be modula ted by a v a r i a b l e f requency dr i ve which

i s cont ro l l e d by a room the r mos ta t . The face and

bypas s dampers could then be cont ro l l ed to ach ieve

a f i x e d d i s c h a r g e a i r t e m p e ra t u re . T h i s wo ul d

make i t p o s s i b l e t o a c h i e v e t h e f a n s a v i n g s a v a i l -

a b l e w i t h a v a r i a b l e a i r v ol um e s y st e m w i t h o u t t h e

o b j e c t i o n ab l e d r o p i n d i s c h a r g e a i r t e m p e ra t u re

and w i th t h e f a l l i n g s e n s i b l e h e a t r a t i o c h a r a c t e r -

i s t i c of the face and bypas s syst em. Al though

s e em i ng t o h o ld p r o m i s e, t h i s s y s t e m h a s n o t y e t

b ee n i n v e s t i g a t e d i n d e p th .

From these p l o t s the impac t of ov e rs i z ing

c h i l l e d w a t e r s y s t e m s c a n b e c l e a r l y se en . W here

a c h i l l e d w a t e r v a l v e o r v a r i a b l e a i r v ol um e s ys -

tem has been used, the syst em

w i l l

always be

o p e r a t i n g a t l ow p a r t l o a d s a n d w i l l tend to

e x p er i e nc e e i t h e r l o s s o f h u m i d i ty c o n t r o l o r

condensat ion problems.

F igures 9 and 10 summar ize the in form at ion

fo r the th r ee co nt ro l me thods d i s cus sed . One can

s e e f ro m F i g u r e 9 t h a t t h e c h i l l e d w a t e r v a l v e

c o n t r o l sh o u l d b e e l i m i n a t e d b e c au s e o f i t s s e n s i -

b l e h e a t r a t i o c h a r a c t e r i s t i c and f ro m F i g ur e LO

o ne ca n s e e t h a t t h e v a r i a b l e a i r f l o w s ho u ld b e

e l imina ted because of

i t s

s u p pl y a i r t e m pe r a tu r e

cha rac te r i s t i c . Only the face and bypas s remains

as a v i ab l e method of module t in g co nt r o l under

extr emes of humidi ty.

The n e x t s t e p i s t o l oo k a t t h e dy na mi c i n -

t e r a c t i o n o f t h e room l o a d s w i t h t h e c o i l a nd i t s

method of cap ac i t y con tro l . The same co i l model

d e s c r i b e d e a r l i e r h as b e en i n c o r p o r a t e d i n a r oo m

s imu la t io n program to do th i s . The ch i l l e d wa te r

v a l v e p ro gr am , f o r i n s t a n c e , a d j u s t s t h e w a t e r

f low through th e co i l i n re sponse t o the room dr y

b u l b t e m p e r a t u r e ( a s su m i n g l i n e a r p o r p o r t i o n a l

c o n t r o l ) u n t i l t h e s e n s i b l e c o o l i n g b e i n g d on e by

the co i l i s ba lanced by the loads on the space .

t t h en o u t p u t s a l l o f t h e p e r t i n e n t d a t a (e.g.,

d ry /we t bu lb t emps fo r room and supply a i r a s

we l l a s room and co i l l oads , e tc .) .

Figures 11 and 12 show t he eq ui l ibr ium room

cond i t ion s which would be reached for a typ ic a l

bu i l d ing a t some commonly found p a r t l oad condi -

t i o n s f o r t h e c h i l l e d w a t e r v a l v e an d f a c e an d

bypass cont ro l sys t ems re spe c t ive ly . As can be

seen , the room i s s l i g h t l y ou t s id e the ASHRAE

c o m f or t r e g io n a t d e s ig n co n d i ti o n s. T h i s r e s u l t s

f rom a s l ig h t ove rs i z in g of the co i l . (One should

note th a t t he Navy des ign c r i t e r i a o f 78-OF and

6 0 r e l a t i v e h u m i d it y c o n t r o l l e d by a t h e r m o s t a t

s e t a t 78-OF a n d a 4-OF t h r o t t l i n g r a n g e

w i l l

i n

f a c t , g i v e c o nd i t i o n s s l i g h t l y o u t s i d e t h e c o m f or t

zone.

The 80/78 (OF/OF) ambient

i s

s e e n t o b e a

problem fo r both methods of co ntr ol . The room

r e l a t i v e h u m i d i t y h as d r i f t e d u p a nd t h e d e w po i n t s

a r e 68.2-OF and 66.5-OF re sp ec t i ve ly . The 75 /69

and 70 /65 g°F/OF) am bien t s a r e ty p ic a l f o r spr ing

and f a l l in Okinawa. As can be seen the face and

bypass sys t em can s e r ve bo th of these loads we l l

b u t t h e c h i l l e d w a t e r v a lv e

s t i l l

c a n n o t m a i n t a i n

h u m i d i t y c o n t r o l .

The f i n a l d a t a p o i n t r e p r e s e n t s

what was commonly found to be the oc cup ant ' s re -

sponse to an uncomfor t ab le cond i t i on ( i. e. , l ow-

e r in g th e th e rmo s ta t t o 72-OF). Both sys t e ms g i ve

room cond i t ion s wi t h in the comfor t zone . The

l o w er r oo m t e m p e r a t u r e h a s r e s u l t e d i n an i n c r e a s e

i n c o i l l o a d o f a p p r o x i m a te l y 1 8 .

A l l

of these

f i n d i n g s a r e c o n s i s t e n t w i t h w h at w as o bs e rv e d i n

the bu i ld ings in Okinawa . The re s u l t s were f r e -

q u e n t l y m as ke d by t h e f a c t t h a t t h e c h i l l e d w a t e r

te mp er at ur e had been r a i s e d from 45-OF t o 55 -OF.

As s een he re , t he occupant s would then gen er a l ly

lo we r t he room th e r m os ta t t o 68-OF o r 70-OF. As a

r e s u l t l i t t l e o r n o co m pr e ss o r en e r g y wo ul d a c t u -

a l l y b e s av ed . The v a r i a b l e a i r f l o w c o n t r o l sy s -

tem has been excluded because

i t

g i v e s su p pl y a i r

tem per atu res 10 to 20-OF below t he room dew po in ts

and i s , hence , unacceptab le.

L a r g e r DX s y s t e m s a r e n o r m a l l y f o un d t o h av e a

s o l e n o i d v a l v e on t h e r e f r i g e r a n t l i n e c o n t r o l l e d

b y a room ( o r r e t u r n a i r ) t h e r m o s t at . T h e re w i l l

f r e q u e n t l y be a h o r i z o n t a l l y s p l i t c o i l w i t h t wo

s o l e n o i d s c o n t r o l l e d b y a t wo s t a g e t h e r m o s t a t .

The f a n i s a l m o s t a l w a y s r u n c o n t i n u o u s l y .

s

m e nt i on e d e a r l i e r , t h e s e s y s t e m s g i v e r a t h e r p o or

h u m i d i t y c o n t r o l du e t o r e e v a p o r a t i o n a nd a r e

p r on e t o c o nd e ns e o n t h e d i f f u s e r s d u r i n g t h e o f f

c y c l e . I f o n e w er e t o p l o t room h u m id i t y v e r s u s

t i m e

i t

would be found to c l imb upward dur ing the

off cy cl e and be brought back down dur ing t he on

cyc le . F ie ld measurements have shown th a t

i t

w i l l

remain unaccepta b ly h igh th roughout bo th pe r iods .

Thi s me thod of co nt r o l i s no t recommended fo r h igh

humidi ty envi ronment s .

Co nt ro l Recommenda ti on s

The method of cap aci ty c on tr ol which was

recommended fo r most sys tems i n Okinawa was on/of f

f a n c o n t r o l . The e x i s t i n g s y s e m s we r e g e n e r a l l y

e i t h e r c h i l l e d w a t er o r r e f r i g e r a n t s o l e n o id

va lv es cont ro l l ed by room the r mos ta t s . A l l f a n s

run cont inuous ly . F igu res 13 and 14 show s imp le

s c h e m a t ic s f o r c h i l l e d w a t e r a n d DX r e s p e c t iv e l y .

F or c h i l l e d w a t e r t h e re c om m en d at i on i s t h a t t h e

c o i l be a l l o we d t o r un w i l d ( c h i l l e d w a t e r v a l ve

f i x e d i n t h e f u l l y op en p o s it i o n ) an d t h e a i r

handl ing un i t f an cyc led on and of f by the room

thermostat . The

DX

u n i t co u ld c o n t i n u e t o c l o s e

t h e s o l e n o i d v a l v e b u t w o ul d a l s o s h u t t h e f a n o f f

d u r i n g t h e o f f c yc l e . I n t h i s way t h e c o i l s wo uld

o p e r a t e a t f u l l c a p ac i t y wh en ev er t h ey a r e i n t h e

on cy cl e and, hence, w i l l b u il d t o f u l l l a t e n t

cap ac i ty under a l l l oads. Kha t t a r , Ramanan and

Swami have shown t h a t fo r

DX

s y s t e m s e x p e r i e n c i n g

25 compres sor run t ime , the cyc le d fa n w i l l de-

l i v e r 2.5 t i m e s a s much l a t e n t c o o l i n g a s t h e

cont inuo us ly running fan (1). The compe t ing op-

t i o n s we r e f o r m s o f m o d u l a t i n g c o n t r o l ( i. e. , t h e

c o m b i n a t i o n o f v a r i a b l e a i r v o lu m e a nd f a c e an d

bypass which has been discusse d). Thi s would have

r e q u i r e d c h a n gi n g o u t t h e a i r h a n d l i n g u n i t s . The

i n c r e m e n t al i n v es t m en t c o u ld n o t b e j u s t i f i e d .

These methods of c on tr ol have some majo r

b e n e f i t s b u t a l s o h av e some s e v e r e l i m i t a t i o n s

th a t mus t be addres sed . On the be ne f i t s ide , t hey

a c h i e v e f a n s a v i n g s w h i ch w ou ld n o t o t h e r w i s e b e

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poss ible . This was found to be of major impor-

tance in most of th e Okinawa bui ldin gs. Another

b e n e f i t i s ac h ie v ed d ue t o t h e f a c t t h a t o u t s i d e

a i r i s br o ug h t i n o n l y i n t e r m i t t e n t l y . W ith many

o f t h e b u i l d i n g s h a vi n g h i g h ( b u t v a r i a b l e ) i n t e r -

n a l p e o p l e l o a d s , t h e e f f e c t i s t o r u n mo re when

the people a re p re sen t and , hence , b r ing i n more

o u t s i d e a i r p r e c i s e l y w hen i t i s needed. (As men-

t i o n e d e a r l i e r , c a r e m u s t b e t a k e n n o t t o ne ga -

t i v e l y p r e s su r i z e t h e sp ac e . T h i s m i gh t r e q u i r e

t h a t a s so c i a t e d e x h a u s t f a n s b e c y c l ed w i t h t h e

a i r handl ing un i t fan .) The combined e f fe c t of

thes e two i t em s in many ca se s amounted to a very

s i g n i f i c a n t e n e r gy s a v i n g s o v e r t h e e x i s t i n g me-

t ho d of c o n t r o l w h i l e a t t h e s am e t i m e i m pr o v i ng

c o m f o r t c o n d i t i o n s i n t h e sp a ce .

By no means a re thes e recommenda t ions appro-

p r i a t e f o r a l l t y pe s of sp a c e s . They w e re a p pr o -

pr i a t e i n Okinawa because of a combina t ion of c i r -

cu mst anc es which may, o r may no t, be commonly

found. F i r s t , i f i n t e r m i t t e n t v e n t i l a t i o n i s n o t

accep tab le some o the r means of c ont ro l should be

found.

t

sh ou l d be p o i n t e d o u t t h a t t h e e x i s t i n g

c o n t in u o u s o p e r a t i o n o f t h e f a n s on D X u n it s i s

no t a ccep tab le i n humid c l ima tes due to the con-

den sat ion problems commonly observed. (The refo re

i t might have o the r wise been necessa ry to go to

some form of modulat ing c ont rol . Thi s would have

i n v o lv e d a m a j o r i n v e s t m e n t i n n ew a i r h a n d l i n g

and pos s ib l y re f r ig e r a t io n equipment. ) Secondly ,

the space should no t be sub je c ted to ex tended

per iods of ex t reme ly l i gh t l oads . Under these

c o n d i t i o n s t h e c o i l s ( an d f a n s )

w i l l

c y c l e t o o

o f t e n a nd p r o p e r d e h u m i d i f i c a t i o n

w i l l

not be

achieved.

I n O ki na wa h i g h a m b i e n t a i r e n t h a l p i e s

and l o o se b u i l d i n g s c om bi ne d t o p r o v i de r e l a t i v e l y

h i g h l o a d s a l a r g e f r a c t i o n o f t h e ti me . F i n a l l y ,

n o i s e f ro m b e l t s a n d e x p a n d i n g/ c o n t r a c t i ng d u c t -

work might a l s o be ob j ec t ion abl e in many types of

spaces . In Okinawa th i s was no t t he case.

I n a d d i t i o n t o t h e s e d e s ig n c o n s i d e r a t io n s

the re a re a number of equipment conce rns which

m i gh t b e l e g i t i m a t e l y r a i s e d .

t i s common know-

l e d g e t h a t s t a r t i n g a nd s t o p p i n g a m o t or

w i l l

d e c r e a s e i t s ex p ec te d l i f e . NEMA h a s r e c e n t l y

p u b l is h e d g u i d e s f o r d u t y c y c l i n g l i m i t a t i o n s

on motors o f va r io us s i ze s and du t i e s (4) . The

n um be r o f s t a r t s an d s t o p s t h a t m i g h t b e e x pe c t ed

wi th th ese me thods of con t r o l appea r to be w i t h in

t h e ac c e p t a b l e l i m i t s f o r a l l o f t h e c a s e s exam -

i n e d . F o r t u n a t e l y

i t

i s f ou nd t h a t t h e t o t a l

t ime requi re d fo r the sys t em to pu l l t he room

tempera ture down p lus t he t ime requi red fo r the

room t o f l o a t ba ck up t o t h e cu t - o n p o i n t i s

r e l a t i v e l y c o n s t a n t and i n s e n s i t i v e t o lo ad . t

i s a l s o w o r th n o t i ng t h a t t h e p r e s e n t w o r th o f

expec ted sav ings would gr ea t l y ou twe igh any rea -

s o n a bl e as s u m p ti o n s a s t o c o s t s f o r p r em a tu r e

m ot or f a i l u r e . W hi le l e s s d e f i n i t i v e i n f o r m a t i on

e x i s t s f o r t h e e f f e c t on b e l t and p u l l ey l i f e ,

t h e c o s t o f r e p la c e me n t f o r t h e s e i t e m s i n s u r e

t h a t t h e s a v i n gs w l l ag ai n overwhelm any reason-

a b l e v a l u e s t h a t o n e m i g h t as su me . The f i r s t y e a r

sav ings f or a t yp ic a l 10 hp motor i n Okinawa (wi th

O. lO/kwh e l ec t r i c i ty ) i s approximately 10001

y e ar . The p r e s e n t w o r th o f t h i s i s on t h e o r d e r

o f 1 4, 00 0 w h i l e t h e r e p l a c e m e n t c o s t f o r a 10

hp motor might be appr oxim ately 400.

I n t h e e v e n t t h a t t h e s p a c e i n q u e s t i o n i s

s u ch t h a t f a n c y c l i n g i s n o t p o s s i b l e , s om e f or m

o f m o d u l at i n g c o n t r o l

w l l

be requ ired . Only

t h o se m e th od s h a vi n g a t t h e i r b a se a f a c e a nd

bypass concep t (e.g., mul t i zone , dua l duc t , e t c . )

w i l l d e l i v e r t h e r i g h t t y p e of s e n s i b l e h e a t r a t i o

a nd s u p p ly a i r t e m pe r a tu r e a t p a r t l o ad c o nd i -

t i o n s . Th e c o m b in a t io n v a r i a b l e a i r vo lu me an d

f a c e an d b y p as s d e sc r i b e d e a r l i e r a n d sh ow n i n

F i g u r e 8 s ee ms t o m e r i t f u r t h e r i n v e s t i g a t i o n a nd

might be a way to ach iev e the fan sa v in gs of

V V

w h i l e m e et i n g t h e p a r t i c u l a r r e q u i r e m e n t s of t h e

h igh humidi ty envi ronment .

PROBLEMS ASSOCIATED WITH SYSTEM SHUTDOWN

When t he equipment cond i t i on ing a spac e

is

s h u t down t h e r e i s t h e p o t e n t i a l f o r m o i s t u r e t o

c o nd e nse on w a l l s , f l o o r s an d o t h e r su r f a c e s i n

the space . When the equipment i s t u rned of f , t h e

dew p o i n t i n t h e sp a c e i m m e d i a t e l y be g i n s t o r i s e .

t t h e sa me t i me t h e s u r f a c e t e m p e r a t u r e of a l l

o b j e c t s i n t h e s p a c e b e g in s t o r i s e and w i l l t end

to fo l low the room dry bu lb . The que s t i on i s s im-

p ly whe the r th e dew poin t w i l l i n c r e a se e no ug h

f a s t e r t o g e t s i g n i f i c a n t l y a he ad o f t h e s u r f a c e

t e m p e r a t u r e s . I f i t does , condense t i on

w l l

occur .

Thi s phenonomon was re por t ed bu t n o t obse rved in

Okinawa . ( I t was, however , ac tu a l ly obse rved i n

t h e c ou r s e o f a s i m i l a r p r o j e c t i n J a c k s o n v i l l e ,

F l o r i d a

.

Fig ure 15 shows the i nc re as e of room dew

p o i n t i f o n e a s su me s a s i m p l e n o c a p a c i t a n c e d i l u -

t i o n m ass b a l a n c e o n t h e r o o m 's m o i s t u r e c o n t e n t .

The room i s a s su me d t o s t a r t a t 78-OF an d 6 0% r e -

l a t i v e h u mi d it y and t h e i n f i l t r a t i n g a m bi e nt a i r

i s a ssu me d t o r e m a i n c o n s t a n t a t a t y p i c a l Ok in aw a

August 5 P.M. value. In fa c t , the room dew po in t

w l l

n o t i n c r e a se t h i s f a s t . K usud a a nd M ik i h av e

a c c o un t e d f o r t h e c a p a c i t a n c e a n d m o i s t u r e a b so r p -

t i o n / r e l e a s e r a t e s o f room f u r n i s h i n g s i n a t y p i -

c a l r e s i d e n c e a n d h a ve sh ow n t h a t t h e e f f e c t c a n

b e a r s i g n i f i c a n t l y o n t h e r oo m 's dew p o i n t ( 5) .

T he q u e s t i o n of su r f a c e t e m p e r a t u r e i s even

more compl i ca t ed . Most room f i n i sh es and fur n i s h-

i n g s a r e c o m p os i t e m a t e r i a l s . The p ro bl em i s t o

p r e d i c t t h e s u r f a c e t e m p e r a t u r e a s t h e r oom d r y

b u l b i n c r e a s e s . T h i s c a n be q u i t e d i f f i c u l t . (The

a u t h o r h a s n o t a t t e m pt e d t o d e a l w i t h t h i s q u a n t i -

t a t i v e l y .

Some gen e ra l qu a l i t a t iv e comments can , how-

ever, be made:

1. By keep ing the room dry bulb as hig h a s

p o s s i b l e t h e s u r f a c e t e m pe r a t u r e s o f o b j e c t s i n

t h e room c a n b e s t a r t e d a t a s a f e v a l u e . The

amb ien t dew po in t a t 5 P.M. on an August day in

Okinawa i s n o t l i k e l y t o ex ce ed 76 OF I f t h e

room temperature

i s

main taine d a t 78-OF no prob-

l ems can occur . (The case which was obse rved in

Ja c k so n v i l l e wa s o ne w he r e t h e c h i l l e d w a t e r t em -

pe r a tu re had been ra i sed and th e occupant s had

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r es po n de d t o t h e i r d i s co m f o r t by m a i n t a i n i n g

68-OF t o 70-OF i n th e space . )

2. Room in te r i o r f in i s he s and furn i sh i ngs

s h o u l d, t o t h e e x t e n t p o s s i b l e , b e c h os e n f o r l ow

the rmal capac i t an ce and poor the rmal conduc t iv i ty .

T h i s w i l l h av e t he e f f e c t o f i n s u r i n g t h a t s u r f a c e

t e m p e r a t u r e w i l l r i s e r a p i d l y a s t h e room w ar ms

up. (Unfor tuna te ly one ge ner a l l y f in ds pa in ted

masonry wa l l s and a co ncr e te s l a b f lo or i n Navy

bui ld ings .

A

good s e l e c t i o n i n a n o f f i c e b u i l d i n g

m i g ht b e c a r p e t on t h e f l o o r w i t h g r a s s c l o t h o r

v iny l wa l l cover ing . )

3. I n t e r i o r p a r t i t i o n w a l l s and f l o o r s a r e

m or e s u s c e p t i b l e t o p r o b l em s t h an e x t e r i o r w a l l s .

Ex ter io r wa l l s ar e (and cont inu e to be) warmed by

t r a n sm i s s io n l oa ds . I n t e r i o r p a r t i t i o n s a r e

cooled on bo th s ide s and con ta in no s to r ed hea t .

4.

A s

can be s een f rom F igure 15 , t he r a t e

a t w hi ch t h e dew p o i n t i n c r e a s e s i s s t r o n g l y i n -

f l ue n ce d by i n f i l t r a t i o n . T h i s c o n s t i t u t e s a n o t h e r

r e as o n f o r m ak in g t h e b u i l d i n g a s t i g h t a s p o s si -

b l e .

PROBLEMS ASSOCIATED WITH STARTUP AFTER PERIOD

OF SHUTDOWN

During a period of shutdown the condi t ion s

o f t h e a i r i n t h e s p a c e w i l l approach those of

t h e a m b i e n t a i r .

A t

t h e t im e of s t a r t u p t he a i r

in the room w i l l b e s i m i l a r t o t h e a m bi e nt a i r

somet ime ear l i er . As sugg es te d by Kusuda and Miki ,

t h e m o i s t u r e s t o r a g e p r o p e r t i e s o f t h e ma t e r i a 1 s

i n t h e s p a c e

w i l l

tend to mo derate any swings of

humidi ty (5) . For th is reason the room dew po in t

w i l l

n o t be a s h i g h a s o n e m i gh t p r e d i c t u s i n g a

no cap aci t ance model. (This even sug ges t s the

advantage of hav ing a l a rg e mois ture s to rag e ca -

p a b i l i t y i n t h e ro om 's f u r n i s h i n g s a nd i n t e r i o r

f i n i s h , a s w i t h c a r p e t and c e r t a i n c e i l i n g m at e-

r i a l s . ) In Okinawa a typ i ca l s t a r t up room condi -

t io n was found t o be 80/ 77 i0F/OF). When t h i s

warm, m o i s t a i r i s p u t i n t o a c o l d c o i l t h e r e s u l t -

i n g su p pl y a i r

w i l l

o f t e n be 15-OF t o 25-OF belo w

th e room's dew poi nt. As an example i f 80/77 room

a i r i s p u t i n t o t h e c o i l s u pp ly a i r

w i l l

b e d i s -

c h a r g e d a t 6 0. 6/ 60 .4 . T h i s i s 15.4 OF b e lo w t h e

dew p o i n t of 7t 0 F.

A l l

o f t h e d i s c u s s i o n i n S ec -

t i o n I1 a b o u t i n d u c t i o n of r oom a i r i s a p p l i c a b l e

an d t h e r e i s a n e x c e l l e n t c h a nc e t h a t c o n d e n s a ti o n

w i l l

o c c c u r a r o un d t h e s u p p l y a i r d i f f u s e r s .

In Okinawa the re spon se was to d i s co nt in ue

unoccupied shutdown. As a r e s u l t a major sav ing s

opp ort uni ty was for fe i t ed . Some method had to be

found to overcome th i s problem.

The key t o any so lu t i on

i s

t o r a i s e t h e s u p -

p l y a i r t e m p e r a t ur e w i t h o u t g i v in g awa y t h e c o i l ' s

l a t e n t c a p a ci t y . The e a r l i e r d i s c u s s i o n o f t h e

v a r i o u s m et ho d s o f c a p a c i t y c o n t r o l s u g g e s t s a

p o s s i b l e s o l u t i o n t o t h e p ro bl em . O nl y t h e f a c e

a nd b y pa s s ga v e e l e v a t e d s u p p l y a i r t e m p e r a t u r e s

w i t h ou t in c r e a s i n g t h e s e n s i b l e h e a t r a t i o . F or

t h e ex a mp le s t a t e d , b y p a s s i n g 50% o f t h e a i r

w i l l

g i v e s u p p l y a i r c o n d i t i o n s o f 6 6. 6/ 65 .1 f0F OF).

The su pp ly a i r has been bro ugh t t o wi t hin 9.4 OF

o f t h e r oo m ' s dew p o i n t w h i l e t h e s e n s i b l e h e a t

r a t i o h a s g o n e f r o m 0 .3 4 t o 0 .3 5. I f 75X o f t h e

a i r i s by pa ss ed t he s u p pl y a i r

w i l l

be 71.8/69.6

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q u a n t i t a t i v e g u i de l i ne s a r e a v a i l a b le t o a s s i s t

the enginee r in making some ve ry impo r t an t des ign

d e c is i o n s. I n p a r t i c u l a r i t was obse rved tha t

m o st o f t h e m et h od s o f c a p a c i t y c o n t r o l n o r m a l l y

u sed a r e i n a p p r o p r i a t e i n t h e h i g h hu m i di t y en -

vironment . More s pe ci f ic al ly most methods were

found to f a i l i n ma i n ta in ing co nt r o l o f room hu-

m i d i t y a n d / o r e x p e r i e n c e c o n d e n sa t i o n p r o bl e ms

u n de r t h e m o st l i k e l y p a r t l o a d co n d i t i o n s . Of

the me thods of modula t ing c on t r o l us ua l ly encoun-

t e red , o n ly fa ce and bypass dampers (w i th an un-

c o n t r o l le d c o i l ) p e rf or me d s a t i s f a c t o r i l y i n b ot h

r e s p e c t s . C h i l l e d w a t e r v a l v e an d v a r i a b l e a i r

v ol um e f a i l e d m i se ra b l y .

The common pr ac t i ce of cyc l in g

DX

c o i l s w i th

r e f r i g e r a n t l i n e s o l e n o i d v a lv e s w h i le a l l o w i n g

t h e f a n t o r u n c o n t i n u o u s l y w as f ou nd t o f a i l i n

b o th r e s p e c t s .

Where condi t ions would pe rmi t , i t

was sug-

g e s t e d t h a t b o t h c h i l l e d w a t e r a nd

DX

u n i t s b e

c o n t r o l l e d by f a n c y c li n g . I n t h e c h i l l e d w a t e r

c a s e t h e c o i l r e ma i ns f u l l y a c t i v a t e d and t h e a i r

h a n d li n g u n i t f a n

i s

cyc led on and off by the room

t h e r m o s t a t . I n t h e

DX

c a s e b o t h t h e s o l e n o i d v a l v e

and the fan a r e cyc led by the room the rmosta t .

A

s i g n i f i c a n t s a v i n g s i n e n e r g y e x p en se a nd a n i m -

provement in room com for t c ondi t ion s

w i l l

r e s u l t

from the implem enta t ion of t hes e recommendations.

The f i n a l pr o bl e m m e n t io n e d ( c o n d e n sa t i o n a t

s t a r t u p a f t e r sh u td o wn ) wa s a l s o f ou nd t o b e of

ma jor s ig n i f i ca nce in Okinawa . In many case s

shutdown of equipmen t dur ing unoccupied p erio ds

had been d i sco nt in ued because the occupant s had

e x p er i e nc e d c o n d en s a ti o n a t t h e t i m e o f s t a r t u p .

C o n t ro l s t r a t e g i e s w e re d ev e lo p ed t o a l l o w a s o f t

s t a r tu p of th e equipment and reduce the chance of

mois ture problems. Through th is , shutdown w i l l

aga in become pos si bl e i n Okinawa.

Repor t s have been sub mi t t ed to the Navy on

the work desc r ibe d i n t h i s pape r. When funded

the recommenda t ions of th i s s tu dy

w i l l

produce an

annua l sav ings of approxima te ly $2.1 mi l l ion fye a r

wi th an inves tment o f appr oxim a te ly $4.8 mi l l i on .

T he b u lk o f t h e s e s a v i n g s i s t h e r e s u l t o f t h e

t wo i t e m s w h ic h a r e t h e p r i m a r y c on c er n o f t h i s

paper ; improved cap ac i ty co nt ro l and shutdown

dur ing unoccupied pe r iods .

There a r e many que s t i ons r a i s ed by the work

o f t h i s c o n t r a c t . Some o f t h e mo re i m p o r t a n t

i t e m s r e q u i r i n g f u r t h e r i n v e s t i g a t i o n i n c l u d e:

1. Ana ly t i ca l and expe r i ment a l work needs

to be done wi t h rega rd to the indu c t ion of room

a i r i n t h e v i c i n i t y o f a s up pl y a i r d i f f u s e r w it h

emphas i s on th e t endency fo r condensa t ion on cool

s u r r ou n d in g s u r f a c e s .

3.

The i s s u e of s o f t s t a r t u p s t r a t e g i e s r e -

q u i r e s c o n s i d e r a b l e a d d i t i o n a l i n v e s t i g a t i o n .

REFERENCES

1. Kh at te r, Mukesh

K.

Ramanan,

N.

Swami,

M.

Fan Cycl ing Ef fe ct s of

A i r

Condi t ione r Mois-

tu r e Removal Per formance i n Warm, Humid C l imatesD' ,

F lo r id a So la r Energy Cente r , Cape Canavera l , FL,

ISA 1985.

2. Spi elv oge l , Lawrence G. Air Condi t ioned

Bui l d ing s i n Humid Cl ima tes , Gui de l ine s fo r De-

si gn , Operat ion, and Maintenance, ARMM Consul-

t a n t s , G louces e r , New Je r sey , Apr i l 1980 .

3.

Nussbaum, Otto

J.

Calcu la t e Counte r -

f low C oi l Pe r formance wi t h a P rogrammable Ca lcu-

l a tor , Hea t ing /P ip in g /Ai r Cond i t ion ing , December

198 3, pp. 49.

4. Energy Management Guide f o r Se le ct io n

and Use of po1iphase Motors , Na t io na l E l ec t r i -

c a l Manufac ture r s Asso c ia t i on , MG-10 1983, Sec t io n

2.8.1.

5.

Kusuda, Tamami, Miki, Masayoshi,

Measurement o f Mois ture Conten t f o r Bui ld ing

I n t e r i o r S u r fa c e s , C e n t e r f o r B u i l d i n g T ec hn o-

logy , Na t i on a l Bureau of S tanda rd s , Washington,

DC,

IS

198 5, pp. 297-311.

2. Improved methods of modula ti ng cap ac it y

c o n t r o l sh o u l d b e i n v e s t i g a t e d . T he c om bi ne d f a c e

6 b y p a ss a nd v a r i a b l e a i r vo lu me sy s te m d i s c u s se d

i s a n e xa m pl e o f t h e t y p e s o f sy s t e m s w hi ch m i g h t

of fe r bo th ene rgy economy and prope r hu midi ty con-

t r o l .

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EWT (OF)

F I G U R E

1

EFFECT ENTE RING WATER

TEMXRATURE

F I r n

EFFECT INIL TRA TION ON ROavl CW IT IO NS

F I W

EFFECT SWAPPING VENTILATION IN IL TR AT IO N

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FLEXIBLE

DIFFUSER - -

 

I

E I L I N G

I

.

I P W E D

R r n

A I R

S UP PL Y A I R

F I G U R E 4

T Y P I C A L C E I L I N G D IF F U SE R

GPCl

F I G U R E 5

KCFM

=

1 9 . 5 B F

=

0 . 0

E F F E C T OF W A T ER F LOW

0 . 1 -

0 ,

GPM = 1 7 0 B F = 0.0

- 5 6

K C F M

F I G U R E 6

E F F E C T O F A I R FLO W

K C F M = 1 9 . 5 G P M

=

1 7 0

B P F

F I G U R E 7

E m C T B Y P A ss if f i

ESL-HH-85-09-05

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F I G U R E

C O MB I N ED F B & VAV SYSTEM

6

SENSIBLE COOLING CAPACITY

Qs

F I G U R E

9

C O I L S E N S I B L E H E A T R A T I O

VS SENSIBLE COOLING C P CITY

ESL-HH-85-09-05

Proceedings of the Second Symposium on Improving Building Systems in Hot and Humid Climates, College Station, TX, September 24-26, 1985

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1 DESIGN CAY

2

TROLBLE PLC WITH 80/78

3.

TRasl

PLC WITH 75/69

4 T W L E PLC WITH 70/65

5 TROlslE PLC WITH 80D 8

T S T A T = ~ ~

Wm:

2=

632.8K BlLH

,   5=7 5 0 . 9 m

HJ VALVE lAOER VPRIWS LOPM

FA R ONTROL

1. DESIGN CAY

2. TROUBLE PLC WITH 80/78

3.

TROUBLE PLC WITH 75/69

4. TROUBLE PLC WITH 70/65

5. TROUBLE PU WITH 80D8,

TSTAT =720F

MITE 4

2

=

648 4

KBTU-I

 

ESL-HH-85-09-05

Proceedings of the Second Symposium on Improving Building Systems in Hot and Humid Climates, College Station, TX, September 24-26, 1985

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F I W

13

FAN CONTRCt - CHILLED

MTER

COIL

T I M

W)

FIGLFX 15

RO M

D W I N T VS TI M AT SW KbN

FIaRE 14

FAN CONlROL DX COIL

ESL-HH-85-09-05

Proceedings of the Second Symposium on Improving Building Systems in Hot and Humid Climates, College Station, TX, September 24-26, 1985