Evaluation of Space Humidity Control
and System Energy Usage for
Conventional and Advanced Unitary
Equipment
Michael J. Witte and Robert H. Henninger
GARD Analytics, Inc.
ASHRAE Winter Meeting, Seminar 39
“Designing for Dehumidification and Mold Avoidance”
January 24, 2006, Chicago, IL (Rev. May 31, 2006)
Revisions on slides 12, 15-18, 20, 27-30, 32-36
Acknowledgements

Preview of ASHRAE Research Project 1254RP



Evaluating the Ability of Unitary Equipment to
Maintain Adequate Space Humidity Levels,
Phase II
Co-funded by U.S. DOE through ARTI
Based on ASHRAE 1121-RP, Phase I Evaluation
Plan, Brandemuehl and Katejanekarn, Univ. of
Colorado at Boulder, June 2001
Rev. May 2006
ASHRAE Seminar, M.J. Witte
2
Objectives


Compare various unitary air conditioning
system humidity control configurations for
application to commercial buildings in terms
of humidity control performance, operating
costs, and lifecycle costs to each other as well
as to conventional unitary equipment
Develop guidelines to help HVAC engineers
and practitioners identify the important
application characteristics and climate factors
that determine which option is most
appropriate
Rev. May 2006
ASHRAE Seminar, M.J. Witte
3
Project Overview

EnergyPlus hourly whole-building simulations







7 Building types
10 Locations
18 System types
2 Ventilation standards
Humidity control and energy use
Economic analysis
Guidelines and recommendations
Rev. May 2006
ASHRAE Seminar, M.J. Witte
4
Building Types







Small Office
Restaurant Dining Area
Large Retail
Theater
Classroom (South exposure)
Classroom-12 Month (South exposure)
Motel Guest Room (South exp.)
Rev. May 2006
ASHRAE Seminar, M.J. Witte
5
Locations





Atlanta, GA
Chicago, IL
Dallas/Fort Worth, TX
Miami, FL
New York, NY
Rev. May 2006





Portland, OR
St. Louis, MO
Washington, DC
Houston, TX
Shreveport, LA
ASHRAE Seminar, M.J. Witte
6
System Types: Case 0-2

Case 0 – Conventional DX System





Case 1 – Base DX System



400 CFM/ton
All CFM/ton values are nominal
“Typical” HVAC design practice
2-stage coil
350 CFM/ton (different equipment than Case 0)
Better dehumidification design practice
Case 2 – DX with Improved Dehumidification


300 CFM/ton
Modified coil, compressor, etc.
Rev. May 2006
ASHRAE Seminar, M.J. Witte
7
System Types: Case 3-4

Case 3 – Base DX with Lower Airflow



300 CFM/ton
Same coil and compressor as Case 1
Case 4 – Air-to-Air Heat Exchanger (AAHX)





350 CFM/ton (Case 1 equipment)
Wrap-around HX
Sensible effectiveness 0.4
No latent transfer
Single-stage coil in all apps
Rev. May 2006
ASHRAE Seminar, M.J. Witte
8
System Types: Case 5

Case 5 – Subcool Reheat Coil





350 CFM/ton
Normal mode same as Case 1
Enhanced dehumidification mode
Standard mfr. option
Switch modes if 50%RH
setpoint not met
Rev. May 2006
ASHRAE Seminar, M.J. Witte
9
System Types: Case 6

Case 6 – Fan Control to Drain Coil





350 CFM/ton
Normal mode same as Case 1
Fan off for short time when compressor cycles off
No moisture re-evaporation
Modeled by turning off latent degradation in DX
coil model – no change in fan power consumption

Ideal case – not achievable in real equipment

Can also be thought of as variable capacity control
Rev. May 2006
ASHRAE Seminar, M.J. Witte
10
System Types: Case 7

Case 7 – Bypass Damper





350 CFM/ton
Normal mode same as Case 1
300 CFM/ton in bypass mode
50 CFM/ton bypassed
Switch modes if 50%RH
setpoint not met
Rev. May 2006
ASHRAE Seminar, M.J. Witte
11
System Types: Case 8

Case 8 – Hybrid DX with Desiccant



400 CFM/ton (Case 0)
Desiccant condition outside air stream
Mixed air to cooling coil
Control to meet
50%RH setpoint
Heat recovery to
exhaust air
Outdoor


Outdoor
Rev. May 2006
ASHRAE Seminar, M.J. Witte
Return
Exhaust
Supply
12
System Types: Case 9

Case 9 – Enthalpy Recovery Wheel





350 CFM/ton (Case 1)
Enthalpy heat recovery OA and exhaust
Bypassed when not beneficial
0.91 sensible
eff. (constant)
0.85 latent
eff. (constant)
Rev. May 2006
ASHRAE Seminar, M.J. Witte
13
System Types: Case 10

Case 10 – DX Outdoor Air Preconditioning

DX Preconditioner






Evaporator in OA stream
Condenser in relief air stream
580 CFM/ton
Standard mfr. option
Run 1st
Main DX System


Rev. May 2006
350 CFM/ton (Case 1)
Run as needed
ASHRAE Seminar, M.J. Witte
14
System Types: Case 11

Case 11 – Base Dual Path

Outdoor air system






2 DX coils in series
300 CFM/ton (Case 3)
150 CFM/ton overall
2 stages each
7.22C (45F) min supply
Return air system



Rev. May 2006
1 DX coil
400 CFM/ton (Case 0)
1 stage (last stage on)
ASHRAE Seminar, M.J. Witte
15
System Types: Case 12

Case 12 – Dual Path + Enthalpy Recovery

Outdoor air system





1 DX coil
350 CFM/ton (Case 1)
2 stages
7.22C (45F) min supply
Return air system



Rev. May 2006
Return
Air
Supply
Air
1 DX coil
400 CFM/ton (Case 0)
1 stage (last stage on)
ASHRAE Seminar, M.J. Witte
16
System Types: Case 13

Case 13 – Dual Path + AAHX

Outdoor air system







2 DX coils in series
AAHX, 0.4 sensible, no latent
300 CFM/ton (Case 3)
150 CFM/ton overall
1 stage each
7.22C (45F) min supply
Return air system



Rev. May 2006
1 DX coil
400 CFM/ton (Case 0)
1 stage (last stage on)
ASHRAE Seminar, M.J. Witte
17
System Types: Case 14

Case 14 – Dual Path + Desiccant

Outdoor air system





1 DX coil
350 CFM/ton (Case 1)
2 stages
7.22C (45F) min supply
Return air system



Rev. May 2006
Outdoor Air
Exhaust
Air
1 DX coil
400 CFM/ton (Case 0)
1 stage (last stage on)
ASHRAE Seminar, M.J. Witte
18
System Types: Case 15-16

Case 15 – Demand Controlled Ventilation


350 CFM/ton (Case 1 equipment)
Pseudo DCV



Minimum OA based on cfm/sf spec from Std. 62
Plus cfm/person OA tracks Occupancy Schedule
Case 16 – Dual Path + DCV


Case 11 equipment
Pseudo DCV – same as above
Rev. May 2006
ASHRAE Seminar, M.J. Witte
19
System Types: Case 17

Case 17 – Base DX with Free Reheat








Case 1 equipment
Overcool to meet 50%RH setpoint
Case 1 sizing – no oversizing for latent
“Free” hot gas reheat from DX condenser
Reheat capacity 100% of condenser heat rejection
No fan penalty for extra reheat coil
Dehumidify only when sensible load
No operation for latent-only load
Rev. May 2006
ASHRAE Seminar, M.J. Witte
20
2 Ventilation Standards

Standard 62-2001


Standard 62.1-2004


Current standard
Ventilation rates



Referenced by many building codes
cfm/sf,
cfm/person
Design occupant density (some change)
Rev. May 2006
ASHRAE Seminar, M.J. Witte
21
2004 vs 2001 Ventilation
2001
2004
Total*
cfm/sf
Case 0**
Base %OA
Total*
cfm/sf
Case 0**
Base %OA
Office
0.14
26%
0.09
18%
Retail
0.30
41%
0.23
44%
School
0.75
53%
0.37
44%
Restaurant
1.43
61%
0.72
43%
Motel
0.09
18%
0.11
22%
Theater
2.14
64%
0.77
37%
Building
*Combined cfm/sf plus cfm/person vent rate **for Atlanta
Rev. May 2006
ASHRAE Seminar, M.J. Witte
22
System Sizing

Sizing simulations using ideal system




Peak sensible coil load



ASHRAE 0.4% dry-bulb day (2001 HOF)
Design ventilation rate
“Purchased Air”
Net (after fan heat)
Plus 10% for oversizing
All systems sized to this net sensible capacity

Except enthalpy wheel sensible capacity credit at
design dry-bulb – smaller DX capacity
Rev. May 2006
ASHRAE Seminar, M.J. Witte
23
Key Modeling Assumptions

Existing simulation tool features



DX coil moisture re-evaporation (continuous fan)
Moisture capacitance (EMPD model)
New simulation tool features developed in
this project


2-Stage DX coil
Multi-mode DX coil



switchable enhanced dehumidification mode
e.g. subcool reheat
Performance curves based on published
manufacturer’s data
Rev. May 2006
ASHRAE Seminar, M.J. Witte
24
Life Cycle Cost

Equipment installed costs




Popular cost estimating guide for base cost
Technical literature for option costs
One option is actual mfr quote
Approximate!



Costs are highly variable, especially for non-standard
options
State average commercial energy costs
15-yr energy cost projections from EIA
Rev. May 2006
ASHRAE Seminar, M.J. Witte
25
Selected Results
Rev. May 2006
ASHRAE Seminar, M.J. Witte
26
2004 Standard Retail in Miami FL
Number of Occupied Hours Zone Relative Humidity >65%
2,500
>70
65-70%
1,500
1,000
500
Rev. May 2006
ASHRAE Seminar, M.J. Witte
Dual Path
DX/Desiccant
Hybrid
Base DX
with
DCV
Dual Path
with
DCV
RetailMIS17
Dual
Path
w/AAHX
RetailMIS16
RetailMIS12
Base DX
Dual Path
w/Dual Path w/Enthalpy
Wheel
RetailMIS15
Base DX
with
OA
Precool
RetailMIS14
Base DX
w/Enthalpy
Wheel
RetailMIS13
Conv.
w/Desiccant
Hybrid
RetailMIS11
Base DX
with
Bypass
Damper
RetailMIS10
Base DX
with
DX Latent
Degrad. Off
RetailMIS09
DX
with
Subcool
Reheat
Coil
RetailMIS08
RetailMIS07
Base DX
Base DX
Lower Airflow with AAHX
300 cfm/ton Sen. Eff.=0.4
Lat. Eff.=0.0
RetailMIS06
RetailMIS04
RetailMIS03
RetailMIS02
Base DX
Base DX
350 cfm/ton w/Improved
Dehumid.
300 cfm/ton
RetailMIS05
Conv. DX
400 cfm/ton
RetailMIS01
0
RetailMIS00
Number Hours >65% RH
2,000
Base DX
w/Free
Reheat
27
2004 Standard Retail in Miami FL
Annual HVAC System Electric Energy Use
450,000
Regen Fan
Supply Fan
DX Cooling
350,000
300,000
250,000
200,000
150,000
100,000
Rev. May 2006
Conv.
Base DX
w/Desiccant w/Enthalpy
Hybrid
Wheel
Base DX
with
OA
Precool
Base DX
Dual Path
w/Dual Path w/Enthalpy
Wheel
ASHRAE Seminar, M.J. Witte
Dual
Path
w/AAHX
Dual Path
DX/Desiccant
Hybrid
Base DX
with
DCV
Dual Path
with
DCV
RetailMIS17
RetailMIS16
RetailMIS15
RetailMIS14
RetailMIS13
RetailMIS12
RetailMIS11
Base DX
with
Bypass
Damper
RetailMIS10
Base DX
with
DX Latent
Degrad. Off
RetailMIS09
DX
with
Subcool
Reheat
Coil
RetailMIS08
RetailMIS07
RetailMIS04
RetailMIS03
Base DX
Base DX
Lower
with AAHX
Airflow
Sen. Eff.=0.4
300 cfm/ton Lat. Eff.=0.0
RetailMIS06
Base DX
Base DX
350 cfm/ton w/Improved
Dehumid.
300 cfm/ton
RetailMIS05
Conv. DX
400 cfm/ton
RetailMIS02
0
RetailMIS01
50,000
RetailMIS00
Electric Energy Use (kWh)
400,000
Base DX
w/Free
Reheat
28
2001 Standard Retail in Atlanta GA
Annual HVAC System Electric Energy Use
350,000
250,000
200,000
150,000
100,000
Rev. May 2006
Base DX
Conv.
w/Desiccant w/Enthalpy
Wheel
Hybrid
Base DX
with
OA
Precool
Dual Path
Base DX
w/Dual Path w/Enthalpy
Wheel
ASHRAE Seminar, M.J. Witte
Dual
Path
w/AAHX
Dual Path
DX/Desiccant
Hybrid
Base DX
with
DCV
Dual Path
with
DCV
RetailATS17
RetailATS16
RetailATS15
RetailATS14
RetailATS13
RetailATS12
RetailATS11
Base DX
with
Bypass
Damper
RetailATS10
Base DX
with
DX Latent
Degrad. Off
RetailATS09
DX
with
Subcool
Reheat
Coil
RetailATS08
RetailATS07
RetailATS04
RetailATS03
Base DX
Base DX
with AAHX
Lower
Sen. Eff.=0.4
Airflow
300 cfm/ton Lat. Eff.=0.0
RetailATS06
Base DX
Base DX
350 cfm/ton w/Improved
Dehumid.
300 cfm/ton
RetailATS05
Conv. DX
400 cfm/ton
RetailATS02
0
RetailATS01
50,000
RetailATS00
Electric Energy Use (kWh)
300,000
Regen Fan
Supply Fan
DX Cooling
Base DX
w/Free
Reheat
29
2001 Standard Retail in Atlanta GA
Number of Occupied Hours Zone Relative Humidity >65%
2,500
>70
65-70%
1,500
1,000
500
Rev. May 2006
ASHRAE Seminar, M.J. Witte
Dual Path
DX/Desiccant
Hybrid
Base DX
with
DCV
Dual Path
with
DCV
RetailATS17
Dual
Path
w/AAHX
RetailATS16
RetailATS12
Base DX
Dual Path
w/Dual Path w/Enthalpy
Wheel
RetailATS15
Base DX
with
OA
Precool
RetailATS14
Base DX
w/Enthalpy
Wheel
RetailATS13
Conv.
w/Desiccant
Hybrid
RetailATS11
Base DX
with
Bypass
Damper
RetailATS10
Base DX
with
DX Latent
Degrad. Off
RetailATS09
DX
with
Subcool
Reheat
Coil
RetailATS08
RetailATS07
Base DX
Base DX
Lower Airflow with AAHX
300 cfm/ton Sen. Eff.=0.4
Lat. Eff.=0.0
RetailATS06
RetailATS04
RetailATS03
RetailATS02
Base DX
Base DX
350 cfm/ton w/Improved
Dehumid.
300 cfm/ton
RetailATS05
Conv. DX
400 cfm/ton
RetailATS01
0
RetailATS00
Number Hours >65% RH
2,000
Base DX
w/Free
Reheat
30
2001 Standard Retail in Atlanta
Number of Occupied Hours Zone Relative Humidity >65%
Continous with Fan Heat &
No Latent Degradation
Cycling with Fan Heat
(Latent Degradation n/a)
Continuous No Fan Heat &
No Latent Degradation
1,200
Continuous No Fan Heat &
With Latent Degradation
Continuous with Fan Heat &
With Latent Degradation
Number Hours >65% RH
1,000
800
600
400
200
0
S00
Conv. DX
400 cfm/ton
Rev. May 2006
S01
Base DX
350 cfm/ton
S02
Base DX
w/Improved Dehumid.
300 cfm/ton
S03
Base DX
Lower Airflow
300 cfm/ton
S04
Base DX
with AAHX
Sen. Eff.=0.4
Lat. Eff.=0.0
ASHRAE Seminar, M.J. Witte
S05
DX with
Subcool Reheat
Coil
S06
Base DX with
DX Latent Degrad.
Off
31
Retail 2004
Humidity Control
Humidity Control (Occupied Hours >65%RH)
Location ==> MI
HO
SH
FW
AT
ST
SL
Case
00
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
System
Conventional DX
Base DX
DX w/Improved Dehumid.
Base DX w/Lower Airflow
Base DX w/AAHX
Base DX w/Subcool Reheat
Base DX w/o Lat. Coil Degrad.
Base DX w/Bypass Damper
Base DX w/Desiccant
Base DX w/Enthalpy Wheel
Base DX w/OA Precool
Dual Path
Dual Path w/Enthalpy Wheel
Dual Path w/AAHX
Dual Path w/Desiccant
Base DX w/DCV
Dual Path w/DCV
Base DX w/Free Reheat
<= 150 hrs
Rev. May 2006
2000 1201 846
356
1713
961 610
314
1475
897 574
357
1261
842 556
390
534
247 134
162
1422
682 416
218
543
283 155
12
1242
640 408
236
0
0
0
0
0
1
5
0
2044 1621 1185 1114
284
145
56
25
0
1
6
0
91
78
24
3
0
0
0
0
465
265 139
190
131
43
13
2
0
1
5
0
196
150
135
188
41
95
0
85
0
0
432
0
0
0
0
27
0
0
151 to 1000 hrs
ASHRAE Seminar, M.J. Witte
200
165
161
176
42
116
35
120
0
0
389
0
0
0
0
58
0
0
292
220
208
208
27
148
28
144
0
0
586
1
0
0
0
41
0
0
1001 to 2000 hrs
NY
78
82
104
129
46
62
14
68
0
0
207
4
0
3
0
45
0
2
CH
PO
54
59
67
85
6
42
3
39
0
0
27
1
0
0
0
3
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
> 2000 hrs
32
Retail 2004
Energy Cost
Relative Annual HVAC Energy Cost vs. Base DX (Case 1)
Location ==> MI
HO
SH
FW
AT
ST
SL
NY
CH
Case
00
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
System
Conventional DX
Base DX
DX w/Improved Dehumid.
Base DX w/Lower Airflow
Base DX w/AAHX
Base DX w/Subcool Reheat
Base DX w/o Lat. Coil Degrad.
Base DX w/Bypass Damper
Base DX w/Desiccant
Base DX w/Enthalpy Wheel
Base DX w/OA Precool
Dual Path
Dual Path w/Enthalpy Wheel
Dual Path w/AAHX
Dual Path w/Desiccant
Base DX w/DCV
Dual Path w/DCV
Base DX w/Free Reheat
< 0% (less energy use)
Rev. May 2006
-1%
0%
-10%
-7%
24%
11%
6%
3%
169%
-26%
10%
-20%
-39%
4%
137%
-9%
-32%
44%
-1%
0%
-11%
-8%
21%
10%
5%
3%
79%
-30%
7%
-19%
-42%
1%
53%
-11%
-33%
32%
1% to 25% (more energy use)
-1%
0%
-10%
-7%
19%
9%
4%
2%
75%
-29%
6%
-18%
-41%
1%
44%
-14%
-34%
24%
-1%
0%
-12%
-8%
19%
10%
5%
3%
47%
-30%
4%
-18%
-42%
1%
20%
-12%
-32%
23%
-1%
0%
-8%
-6%
14%
7%
4%
2%
61%
-30%
8%
-17%
-41%
-2%
20%
-18%
-38%
15%
0%
0%
-6%
-4%
9%
5%
2%
1%
18%
-42%
6%
-13%
-51%
-3%
-9%
-26%
-40%
10%
0%
0%
-6%
-4%
10%
5%
3%
1%
14%
-46%
5%
-12%
-54%
-1%
-11%
-25%
-38%
10%
26% to 50% (more energy use)
ASHRAE Seminar, M.J. Witte
0%
0%
-10%
-8%
13%
6%
3%
1%
6%
-32%
8%
-21%
-44%
-9%
-14%
-20%
-42%
10%
0%
0%
-7%
-5%
9%
4%
2%
1%
-11%
-46%
7%
-13%
-55%
-5%
-30%
-26%
-40%
7%
PO
0%
0%
-8%
-6%
9%
4%
2%
0%
-2%
-18%
9%
-18%
-28%
-10%
-15%
-25%
-45%
1%
>50% (more energy use)
33
Retail 2004
Life Cycle Cost
Criteria
Best Cases (Case ID Number)
Location ==> MI
HO
SH
FW
AT
Minimum Energy Cost (EC)
12
12
12
12
12
Minimum EC, <=150 hrs RH>65%
12
12
12
12
12
Minimum Life Cycle Cost (LCC)
12
12
12
12
12
Minimum LCC, <=150 hrs RH>65%
12
12
12
12
12
Ratio Min LCC<=150 to Case 01 LCC
0.8
0.7
0.7
0.7
0.8
MI
= Miami FL
HO
= Houston TX
SH
= Shreveport LA
FW
= Fort Worth TX
AT
= Atlanta GA

ST
12
12
09
09
0.7
ST
SL
NY
CH
PO
SL
12
12
09
09
0.7
=
=
=
=
=
NY
CH
PO
12
12
16
12
12
16
12
09
09
12
09
09
0.8
0.7
0.9
Washington DC
St. Louis MO
New York NY
Chicago IL
Portland OR
Adequate humidity control and LOWER LCC


Case 12 - Dual Path w/Enthalpy Wheel
Case 9 - Base DX w/Enthalpy Wheel
Rev. May 2006
ASHRAE Seminar, M.J. Witte
34
Restaurant 2004
Humidity Control
Humidity Control (Occupied Hours >65%RH)
Location ==> MI
HO
SH
FW
AT
ST
SL
Case
00
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
System
Conventional DX
Base DX
DX w/Improved Dehumid.
Base DX w/Lower Airflow
Base DX w/AAHX
Base DX w/Subcool Reheat
Base DX w/o Lat. Coil Degrad.
Base DX w/Bypass Damper
Base DX w/Desiccant
Base DX w/Enthalpy Wheel
Base DX w/OA Precool
Dual Path
Dual Path w/Enthalpy Wheel
Dual Path w/AAHX
Dual Path w/Desiccant
Base DX w/DCV
Dual Path w/DCV
Base DX w/Free Reheat
<= 150 hrs
Rev. May 2006
4473
4483
4549
4548
3790
4230
3727
4362
17
2498
4302
4254
674
1729
0
4521
2542
85
3518
3498
3598
3541
3013
3175
2713
3308
97
1852
3759
3259
649
1300
0
3532
1628
217
2518
2506
2612
2560
2101
2281
1892
2372
3
1049
3080
2264
308
795
0
2680
884
155
1903
1917
2117
2070
1835
1551
886
1709
1
1327
2634
1104
110
249
0
2435
202
40
1827
1839
1955
1932
1689
1627
1083
1729
0
740
2183
1519
270
616
0
2026
620
116
151 to 1000 hrs
ASHRAE Seminar, M.J. Witte
1354
1363
1445
1427
1229
1177
831
1276
0
655
1936
1115
162
510
0
1592
562
40
NY
1308
862
1296
885
1395
957
1369
946
1083
876
1126
793
815
477
1205
841
5
0
461
645
2146
813
1094
698
149
213
344
381
0
0
1606 1095
418
446
49
91
1001 to 2000 hrs
CH
PO
661
670
738
729
593
618
346
638
0
307
649
544
121
282
0
909
284
30
2
2
6
6
2
2
0
2
0
6
0
10
6
7
0
2
0
0
> 2000 hrs
35
Restaurant 2004
Life Cycle Cost
Criteria
Best Cases (Case ID Number)
Location ==> MI
HO
SH
FW
AT
Minimum Energy Cost (EC)
16
16
16
16
16
Minimum EC, <=150 hrs RH>65%
17
14
14
12
17
Minimum Life Cycle Cost (LCC)
12
12
12
12
12
Minimum LCC, <=150 hrs RH>65%
17
14
14
12
17
Ratio Min LCC<=150 to Case 01 LCC
1.4
1.9
1.8
0.7
1.2
MI
= Miami FL
HO
= Houston TX
SH
= Shreveport LA
FW
= Fort Worth TX
AT
= Atlanta GA

SL
16
12
09
12
0.6
=
=
=
=
=
NY
CH
PO
16
16
16
14
12
16
12
12
15
17
12
15
1.1
0.6
0.7
Washington DC
St. Louis MO
New York NY
Chicago IL
Portland OR
Adequate humidity control but HIGHER LCC



ST
16
14
12
17
1.1
ST
SL
NY
CH
PO
Case 17 - Base DX w/Free Reheat
Case 14 - Dual Path w/Desiccant
Less-adequate humidity control but LOWER LCC

Case 12 - Dual Path w/Enthalpy Wheel
Rev. May 2006
ASHRAE Seminar, M.J. Witte
36
Trends

Relative humidity control across system
types


Fairly constant from location to location for
a given combination of building type and
ventilation standard
Overall number of high humidity hours
changes across the board when changing
locations, but the relative pattern of
humidity control remains very similar
Rev. May 2006
ASHRAE Seminar, M.J. Witte
37
Challenging Applications



Restaurant, Theater, Motel in humid
climate
Large number of hours with moisture
load but little or no sensible load –
morning, evening, night
Active humidity control required


Desiccant
Reheat
Rev. May 2006
ASHRAE Seminar, M.J. Witte
38
Less Challenging Applications



Retail, Office, School in humid climate
Restaurant, Theater, Motel in moderate
climate
Load reduction for cost savings and less
humidity


Enthalpy Wheel
DCV
Rev. May 2006
ASHRAE Seminar, M.J. Witte
39
Conclusions




Generalizations based on one set of
assumptions
Results tables allow some extrapolation
to other cases
New simulation tool features provide
designers tool to evaluate specific
applications
Questions . . .
Rev. May 2006
ASHRAE Seminar, M.J. Witte
40