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Efficiency & Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

Contract No. DE-AC36-08GO28308

Using EnergyPlus to Perform 

Dehumidification Analysis on 

Building America Homes 

Preprint 

Xia Fang, Jon Winkler, and Dane Christensen

National Renewable Energy Laboratory

To be published in the HVAC&R Journal

June 2011

Journal Article

NREL/JA-5500-49899 

March 2011
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1

Using EnergyPlus to Perform 

Dehumidification Analysis on

Building America Homes

ABSTRACT 

A parametric study was conducted using EnergyPlus version 6.0 to investigate 

humidity issues on a typical mid-1990s reference home, a 2006 International Energy 

Conservation Code home, and a high-performance home in a hot-humid climate. The 

impacts of various dehumidification equipment and controls are analyzed on the high 

performance home. The study used the Walker and Wilson (1998) infiltration model to 

examine the combined effects of infiltration and mechanical ventilation with balanced 

and unbalanced mechanical ventilation systems. Indoor relative humidity excursions 

were examined; specifically, the number of excursions, average excursion length, and 

maximum excursion length. Space relative humidity, thermal comfort, and whole-house 

source energy consumption were analyzed for indoor relative humidity set points of 50%, 

55%, and 60%.

The study showed and explained why similar trends of high humidity were observed 

in all three homes regardless of energy efficiency, and why humidity problems are not 

necessarily unique in high-performance homes. Thermal comfort analysis indicated that 

occupants are unlikely to notice indoor humidity problems. The study confirmed that 

supplemental dehumidification should be provided to maintain space relative humidity 

below 60% in a hot-humid climate. All modeled supplemental dehumidification options 

successfully controlled space relative humidity excursions, yet the increase in wholehouse energy consumption was much more sensitive to the humidity set points than the 

chosen technology option. 

INTRODUCTION

As the Building America (BA) program begins constructing homes that achieve 50% 

and greater source energy savings over typical mid-1990s construction, proper modeling 

of whole-house latent loads and operation of humidity control equipment has become a 

high priority. A 50% savings home has significantly reduced space-sensible cooling loads 

because of its high-performance envelope, ENERGY STAR® appliances, and energyefficient lighting. An energy-efficient home must also manage a different latent load 

profile compared to conventional construction because of reduced natural infiltration, 

added ASHRAE Standard 62.2 code-compliant mechanical ventilation, and ENERGY 

STAR appliances. 

Walker and Sherman (2007) showed that, for an International Energy Conservation 

Code (IECC) 2005 code-compliant home, adding ASHRAE 62.2-2004 (ASHRAE 2004a) 

code-compliant ventilation systems yielded insignificant changes to average indoor 

relative humidity (RH) except in a hot-humid climate. An average increase of 5%–10% 
2

RH was observed for the hot-humid climate of Houston, yet the occurrence of hours 

above 70% RH was reduced.

Rudd and Henderson (2007) presented field data collected from 43 homes in various 

climate regions throughout the United States, including six hot-humid cities. They 

observed that periods of high space RH generally occurred when the air-conditioner 

(A/C) ran at part-load conditions. The study concluded that low sensible heat gain, 

coupled with continuous mechanical ventilation in high-performance homes, significantly 

increased the number of hours requiring supplemental dehumidification.

Henderson et al. (2008) conducted a TRNSYS study to analyze space A/C equipment 

with and without humidity control strategies in several hot-humid cities. The study used 

the TRNSYS 16 multi-zone type 56 building model to analyze either variable natural 

infiltration using the Sherman-Grimsrud model (ASHRAE 2009a) or constant infiltration 

and mechanical ventilation as prescribed by ASHRAE 62.2-2004, but did not examine 

the combined effects of natural infiltration and mechanical ventilation. Their study 

included a Home Energy Rating System (HERS) reference home (which was consistent 

with the 2004 IECC minimum efficiency standards) and a high-efficiency home, which 

had slightly lower performance than the high-performance home used in the current 

study. Their study also concluded that explicit dehumidification must be provided to 

maintain space RH below 60%. 

We used new features in EnergyPlus version 6.0 (DOE 2010) to conduct a parametric 

study for analyzing the impacts of various dehumidification equipment and control 

strategies on a high-performance home in Houston at the 50% source energy savings 

level. A 50% savings home has significantly reduced whole-house energy consumption, 

so dehumidification equipment energy use becomes a larger portion of whole-house 

energy consumption. Improved simulation of A/C and dehumidification system 

interaction is expected to support the optimization of a home’s features for durability, 

healthy indoor air quality, and minimization of energy use and system cost. A typical 

mid-1990s reference home and a 2006 IECC code-compliant home served as basis for 

comparison.

The paper presents analysis results, focusing on RH “excursions,” which are defined 

as unique events of indoor RH above a threshold. For each mechanical system and home 

type in this study, the number of excursions, average excursion length, and maximum 

excursion length were recorded. Mold growth can begin during an excursion above 70% 

RH in 24 to 48 hours (EPA 2010, Occupational and Environmental Epidemiology 2005), 

given the appropriate temperature, mold spores, and food source. Although mold growth 

is directly related to the humidity and temperature of the surfaces rather than of the 

indoor air, the two are closely related. One 24-hour long RH excursion promotes much 

more mold growth than 24 intermittent 1-hour long RH excursions, and therefore, does 

much more harm to the house. Mold reduces the home’s durability and degrades indoor 

air quality, so significant excursions must be controlled.

The impacts of different humidity set points (50%, 55%, and 60% RH) on RH 

excursions and energy consumption were studied for the 50% savings home parametric 

cases with explicit humidity control equipment. These set points are commonly used on 

dehumidification equipment for mold and dust mite control in houses (ASHRAE 2009a). 
3

Obviously the dehumidification equipment will consume more energy to meet the lower 

RH set point, but the space humidity control may become more effective. Additionally, a 

lower RH set point may require larger dehumidification equipment. 

Our study examined combined infiltration and mechanical ventilation effects with 

balanced and unbalanced mechanical ventilation systems in EnergyPlus. We used the 

infiltration model from Walker and Wilson (1998), which was developed specifically for 

residential buildings and includes more detailed coefficients than the Sherman-Grimsrud 

method. We examined living space RH, thermal comfort, and whole-house energy 

consumption. 

MODELING APPROACH AND ASSUMPTIONS

Descriptions of Homes 

Three homes are used in the analysis: a typical mid-1990s reference home, which is 

described as the BA Benchmark Home (Hendron and Engebrecht 2010), a 2006 IECCcompliant house (ICC 2006), and a high-performance home (50% source energy savings 

level whole-house technology package developed using a cost and performance analysis) 

(Anderson and Roberts 2008). The geometry from Anderson and Roberts was used for all 

three homes. The house used in the analysis was a two-story, three-bedroom, 2,500-ft2

(232 m2

), slab-on-grade structure. Shelter class 3 was assumed for modeling infiltration 

and it was assumed the house did not contain a flue. It was assumed to be east facing with 

an 18% window-to-floor area ratio. The homes’ parameters with greatest impact on living 

space humidity levels are shown in Table 1. 

Table 1: Features of the Three Homes Used In the Analysis

Reference Home IECC 2006 Home

(Climate Region 2)

High-Performance 

Home

Wall Assembly 2 × 4, 16” on center

R-11 cavity

2 × 4, 16” on center

R-13 cavity

2 × 6, 24” on center

R-21 cavity

Ceiling Assembly R-20 assembly R-30 assembly R-30 assembly

Window U-Value 1.0 Btu/hr-ft2

-°F

(5.7 W/m2-K)

0.75 Btu/hr-ft2-°F

(4.3 W/m2-K)

0.35 Btu/hr-ft2-°F

(2.0 W/m2-K)

Window Solar Heat Gain 

Coefficient 0.79 0.40 0.26

Specific Leakage Area 0.00057 0.00036 0.00015

Duct Location Vented Attic Vented Attic Conditioned Space

Duct Insulation R-5 R-8 N/A

Duct Leakage 10% Supply Leakage

5% Return Leakage

10% Supply Leakage

5% Return Leakage N/A

Average Daily Internal 

Moisture Generation 15.0 lb/day (6.8 kg/day) 15.0 lb/day (6.8 kg/day) 14.8 lb/day (6.7 kg/day)

Heat Pump Rating SEER 10, HSPF 7.2 SEER 13, HSPF 8.1 SEER 15, HSPF 8.8

Mechanical Ventilation Spot Vents Only 100% ASHRAE 62.2 100% ASHRAE 62.2

The average daily internal moisture generation listed in Table 1 follow the BA 

Benchmark-prescribed load profiles for water use fixtures (shower, bath, and sinks) and 

appliances (clothes washer and dishwasher). The slight difference in the internal moisture 

generation among the three homes is due to ENERGY STAR appliances. Several studies 

in the literature assumed similar average daily internal moisture generation:
4

• Tenwolde and Walker (2001) found an average moisture generation of 15.9 lb/day 

(7.2 kg/day) for a house with one to two adults, with a standard deviation of 4.9 

lb/day (2.2 kg/day) from multiple studies. The first child introduces an additional 

8.8 lb/day (4 kg/day), the second child introduces 4.4 lb/day (2 kg/day), and each 

additional child introduces 2.2 lb/day (1 kg/day). The data set is adopted in 

ASHRAE Standard 160 “Design Criteria for Moisture Control in Buildings” to 

derive design conditions (ASHRAE 2009b).

• Walker and Sherman (2007) examined several sources of information and used 

14.3 lb/day (6.5 kg/day) for their simulation. The number is based on the 

assumption that moisture generated by bathing, cooking, and dishwashing 8.8 

lb/day (4 kg/day) for a family of four (Emmerich et al. 2005)) is directly 

exhausted by spot ventilation, and thus needs to be substracted from a total daily 

30.4 lb/day (13.8 kg/day) (ASHRAE 2009b). Additionally, their simulated house 

was occupied for only two-thirds of the day.

The heating and cooling set points are defined by BA Benchmark definition at 71°F 

(21.67°C) for heating and 76°F (24.4°C) for cooling. The effect of RH set point (when 

applicable) was examined and three RH set points were used: 50%, 55%, and 60%. Based 

on the BA Benchmark definition, the house had three occupants whose schedules resulted 

in fewer occupants during the daytime hours. Schedules and assumptions are consistent 

among the three homes and can be found in the BA Benchmark definition.

A moisture capacitance model is used in the analysis with a whole-house moisture 

capacitance multiplier of 15 (EPA 2001). This multiplier is also consistent with values 

used in previous studies for simulation of residential buildings (Henderson 2010). The 

EnergyPlus humidity capacitance multiplier was used to alter the effective moisture 

capacitance of the zone air volume and provided a mechanism to include the moisture 

buffering effect of building materials and furnishings.

High Performance Home Dehumidification Parametric Case Descriptions 

Parametric cases 0 through 9 are on the high-performance home in Houston. A 

properly sized 2-ton (7-kW) A/C unit with a sensible heat ratio of 0.8 was selected for all 

cases. Proper sizing of the A/C is paramount in real practice and modeling. EnergyPlus 

uses the latent heat degradation model (Henderson et al. 1992), so an oversized A/C 

system with shorter run time will remove less moisture.

Case 0 – A/C Only. Case 0 represents the high-performance home equipped with a 

typical air conditioner for space conditioning (see Table 1). The cooling set point is 

constant at 76°F (24.4°C). 

Case 1 – Thermostat Reset. Despite the A/C system maintaining a well-controlled 

cooling set point of 76°F (24.4°C), there are hours when space RH reaches high levels. 

An “enhanced” A/C control strategy commonly quoted is to overcool the space by 3°F 

(1.67°C) when the living space RH exceeds 60%. Overcooling the living space during 

high humidity periods increases A/C run time; thus, it removes more moisture and 

reduces the space humidity ratio. However, from a psychrometric standpoint, reduced 

space humidity ratio combined with reduced air temperature can result in continued high 

space RH, making overcooling periods excessively long. This interaction effect is 
5

analyzed in the next section. In reality, overcooling the living space can exacerbate 

humidity problems because a larger outdoor-indoor temperature difference results in 

more moisture flow from the warm side to the cold side of the building envelope. With 

reduced indoor air temperature, interior surface temperatures also decrease and the 

surface RHs increase, approaching 70% (Lstiburek 1993). These issues, though currently 

not analyzed using EnergyPlus, are serious practical concerns that can make Case 1 an 

unrecommended strategy. 

Case 2 – A/C with Energy Recovery Ventilator (ERV). In the summertime, an 

ERV cools and dries the hot and humid outside ventilation air by exchanging heat and 

moisture into the (conditioned) house exhaust air. In a hot-humid city such as Houston, 

where mechanical ventilation increases space RH on average by 5%–10% (Walker and 

Sherman 2007), using an ERV for mechanical ventilation should reduce the house 

humidity level. Rudd and Henderson (2007) revealed an ERV may have helped control 

the latent load from ventilation; however, the ERV was insufficient to control humidity 

alone or when the A/C was running at part-load conditions. The modeled ERV is a static 

enthalpy heat exchanger with an average winter and summer effectiveness of 75% and 

60%, respectively. The supply and exhaust fans are assumed to have balanced flow rates 

equal to ASHRAE 62.2 requirements. Explicit humidity controls were not used to control 

the ERV.

Case 3 – Heat Exchanger (HX)-Assisted A/C. An HX-assisted cooling coil (CC) 

has an HX wrapped around the direct-expansion (DX) CC (see Figure 1). The A/C inlet 

air is first precooled by the passive HX. This process improves the latent removal 

performance of the DX CC by allowing it to further depress the supply air dewpoint 

temperature. The cold air leaving the coil is then rewarmed by the passive HX and exits 

the equipment. Similar to the Henderson et al. (2008) TRNSYS model, a heat pipe HX 

was modeled with an average sensible effectiveness of 32%. 

Figure 1: Heat Exchanger-Assisted Cooling Coil

Case 4 – A/C with Condenser Reheat. A DX CC with condenser reheat can actively 

control space temperature and RH (see Figure 2). Under normal operation, the A/C 

operates to meet the space thermostat cooling set point. When the space RH exceeds the 

humidistat RH set point, the DX CC further reduces the leaving air temperature to meet 

the space RH set point. The overcooled and dehumidified leaving air is then reheated by 

the condenser coil downstream. 

Heat Exchanger

DX CC

Room Air

Supply
6

Figure 2: A/C with Condenser Reheat

The component model available in EnergyPlus version 6.0 to simulate this process is 

a desuperheater; however, the heat reclaim efficiency is limited to 30%. Thus, the system 

cannot simultaneously meet the cooling space temperature and humidity set points. To 

overcome this limitation, an unmetered gas heating coil was used to reheat the supply air 

(simulating condenser waste heat recovery) downstream of the DX CC. The condenser 

coil inlet air conditions were adjusted during dehumidification mode using the DX CC 

outlet and outdoor air temperatures. 

During dehumidification mode, EnergyPlus reheats the CC outlet air to meet the 

space heating set point. In actual residential equipment, the reheat temperature during 

dehumidification mode is either the cooling set point or 0.5°F (0.28°C) below cooling set 

point (Henderson et al. 2008). Besides occupant discomfort, overcooling the living space 

during dehumidification mode results in the same problem described in Case 1. This 

problem worsens because the living space temperature is further reduced to the heating 

set point. To avoid this problem, an energy management system procedure was created in 

EnergyPlus to raise the space heating set point to the cooling set point from April to 

October. Because the modeled package needs to overcool and dehumidify the entire 

cooling supply air volume to meet the space humidity set point, an excessive amount of 

A/C energy may be required.

Case 5 – A/C with Desiccant Wheel Dehumidifier. A desiccant dehumidifier 

regenerates the desiccant wheel with heat rejected by the condenser (see Figure 3). By 

separating the supply airstream from the regenerative airstream, the unit supplies cool 

and dry air to the home and reduces A/C run time. A room air recirculating desiccant 

wheel dehumidifier was used in the model. Performance curves used for both the 

desiccant wheel and the DX coil were generated using the manufacturer’s publicly 

available sizing software.

At Air-Conditioning, Heating and Refrigeration Institute (AHRI) rated conditions, the 

system simulated has a moisture removal rate of 120 pints/day (56.8 L/day) and an 

energy factor of 7.0 pints/kWh (3.3 L/kWh) at an air flow rate of 200 cfm (0.09447 m3

/s) 

for process and regeneration sides. 

DX CC

SF Room Air Supply Reheat Coil

Compressor Condenser
7

Figure 3: Desiccant Wheel Dehumidifier

Case 6 – A/C with High-Efficiency DX Dehumidifier. A common solution for 

controlling RH is to use a standalone vapor compression dehumidifier. We used three 

dehumidifiers to determine the RH control and energy consumption of different size 

units.

Table 2: High-Efficiency Dehumidifier Test Cases

Moisture Removal Rate, 

pints/day (L/day)

Energy Factor, 

pints/kWh (L/kWh)

High-Efficiency Dehumidifier #1 (Small) 65 (30.8) 4.2 (2.0)

High-Efficiency Dehumidifier #2 (Medium) 90 (42.6) 5.3 (2.5)

High-Efficiency Dehumidifier #3 (Large) 150 (71.0) 7.8 (3.7)

We used performance data from Christensen and Winkler (2009) and assumed that 

the normalized performance curves generated from test data could be applied to a 

smaller, similarly configured unit. The DX dehumidifier supplies warm, dry air to the 

living space because the latent heat removed from the airstream and the electric power 

consumed by the unit is rejected as heat to the supply airstream. As a result, operating a 

DX dehumidifier will increase A/C cooling run time and offset heat pump heating 

demand.

Case 7 – A/C with Standard-Efficiency DX Dehumidifier. A standard efficiency 

dehumidifier was included to determine the energy savings from using a high-efficiency 

unit. The standard efficiency unit was assumed to have the same capacity as the smallest 

high-efficiency unit (65 pints/day, 30.8 L/day) at reduced energy factor of 3.2 pints/kWh 

(1.5 L/kWh) (minimal ENERGY STAR cutoff point). Experimental test data generated 

by the National Renewable Energy Laboratory for a similar unit were used to create the 

necessary performance curves. 

Case 8 – A/C with ERV and High-Efficiency DX Dehumidifier. This case 

combines technologies used in Case 2 and the smallest dehumidifier used in Case 6.

Case 9 – A/C with ERV and Standard-Efficiency DX Dehumidifier. This case 

combines technologies used in Cases 2 and 7.

Desiccant Wheel

DX CC

Condenser

SF

EF

Room Air Supply

Regen
8

MODELING RESULTS AND ANALYSIS

Predictions of Relative Humidity Excursions

Tables 3 and 4 show simulation results for RH excursions above 60% and 70% for 

the reference home, 2006 IECC home, and high-performance home without humidity 

control equipment. These homes undergo lengthy RH excursions above 60% and 70%, 

and thus are prone to mold growth. Reducing the thermostat when the space RH exceeds 

60% (Case 1) does little to reduce the number of hours with high humidity levels.

Incorporating an ERV (Case 2) into the house reduces the overall number of hours of 

high RH, but does little to reduce the maximum excursion lengths. The ERV’s ability to 

reduce the overall number of high RH hours is a result of the ventilation latent load being 

a significant percentage of the overall latent load of the building. Of the three passive 

techniques (Cases 1–3), the HX-assisted CC (Case 3) best controls the space RH. Even 

though the number of hours of high RH is significantly reduced in Case 3, the maximum 

excursion length in Case 3 is 66 hours.

Table 3: RH Excursions for the Reference Home and IECC 2006 Home

Case

Description

Number of Hours Number of 

Excursions

Average Excursion 

Length (h)

Maximum Excursion 

Length (h)

> 60% > 70% > 60% > 70% > 60% > 70% > 60% > 70%

Reference Home 1,729 96 139 17 12 6 86 27

2006 IECC Home 2,069 83 162 17 13 5 90 14

Table 4: RH Excursions for the High-Performance Home w/o Humidity Control Equipment

Case Description Number of Hours Number of 

Excursions

Average Excursion 

Length (h)

Maximum Excursion 

Length (h)

> 60% > 70% > 60% > 70% > 60% > 70% > 60% > 70%

0 A/C Only 1,528 39 103 6 15 6 105 19

1 Thermostat Reset 1,666 13 93 1 18 13 99 13

2 A/C w/ERV 688 37 60 3 11 12 101 16

3 HX-Assisted A/C 353 16 30 2 12 8 66 15

Table 5 shows the RH excursions above 60% for the various types of humidity 

control equipment controlled to the three humidistat set points of 50%, 55%, and 60%. 

All types of active humidity control equipment control space RH levels very well. The 

RH did not exceed 70% for cases 4–9 with the listed humidistat RH set points. The 

number of hours when the living space RH exceeds 60% increases as the humidistat RH 

set point increases from 50% to 60% for all cases. This is because the equipment does not 

have the capacity to maintain the RH set point for all hours of the year. As the set point 

increases, the likelihood of the living space RH exceeding 60% also increases. The 

number of hours when the living space RH exceeds 60% is highest for the A/C system 

with condenser reheat (Case 4); however, the RH exceeds 60% for only short periods 

throughout the year. Using different humidistat set points (50%, 55%, or 60%) has 

minimal impact on space air RH excursions above 60% or 70%, assuming well-mixed 

room air conditions. A small dehumidifier controls the room RH as well as a large 

dehumidifier. 
9

Table 5: RH Excursions Above 60% for Humidistat RH Set Points of 50%, 55%, and 60%*

Case Description

Number of Hours > 

60% RH

Number of 

Excursions

Average Excursion 

Length (h)

Maximum Excursion 

Length (h)

50% 55% 60% 50% 55% 60% 50% 55% 60% 50% 55% 60%

4 A/C w/Condenser 

Reheat 0 36 88 0 17 63 0 2.1 1.4 0 4 6.7

5

A/C w/Desiccant 

Wheel 

Dehumidifier

0 0 40 0 0 48 0 0 0.8 0 0 5

6.1

A/C w/Small

High-Efficiency 

Dehumidifier

0 0 3 0 0 18 0 0 0.2 0 0 0.3

6.2

A/C w/Medium

High-Efficiency

Dehumidifier

0 0 3 0 0 18 0 0 0.2 0 0 0.3

6.3

A/C w/Large

High-Efficiency

Dehumidifier

0 0 1 0 0 7 0 0 0.2 0 0 0.2

7

A/C w/StandardEfficiency

Dehumidifier

0 0 5 0 0 22 0 0 0.2 0 0 0.5

8

A/C w/ERV and

Small HighEfficiency

Dehumidifier

0 0 1 0 0 7 0 0 0.2 0 0 0.2

9

A/C w/ERV and

Standard

Efficiency 

Dehumidifier

0 0 2 0 0 13 0 0 0.2 0 0 0.3

* A humidistat deadband of ±2% RH was assumed in determining excursion statistics for the 60% RH set point.

Henderson et al. (2008) examined humidity in a HERS reference home. That 

simulation had an internal moisture generation rate of 10.4 lb/day (4.7 kg/day) and 

assumed a year-round constant ventilation rate of 97.5 cfm (0.046 m3/s). The simulation 

results predicted 1,557 hours when the space RH exceeded 60%. The 2006 IECC home in 

the current study is similar to this house. The differences include additional internal 

moisture generation, a specific leakage area of 0.00036, modeling of the interaction 

effects between natural infiltration (using the Walker and Wilson infiltration model), and 

mechanical ventilation. Based on these differences, the increase in the number of hours 

when the space RH exceeded 60% from 1,557 to 2,069 is expected. 

The results presented in Tables 3 and 4 demonstrate that indoor humidity problems 

are not unique to high-performance homes and likely appear in conventional homes as 

well. Previous studies suggested humidity problems might be unique to high-performance 

homes because the sensible load is drastically reduced, but the latent load is changed little 

(Rudd and Henderson 2007). Therefore, A/C can no longer be expected to remove the 

necessary amount of moisture from the living space in a high-performance home. The 

A/C run times, coupled with the infiltration and ventilation latent loads from the current 

study, can explain why the humidity problems are not unique to the high-performance 

home. 

The living space RH exceeded 60% for the most hours during April, when the A/C 

run times for the reference home, IECC 2006 home, and high-performance home were 

130, 109, and 83 hours, respectively. Thus, for all three homes the A/C did not run for a 
10

significant amount of time (compared to July when the A/C ran two to three times

longer). Figure 4 shows the number of hours when the living space RH exceeds 60% as a 

function of A/C run time fraction (DOE 2010). Nearly 50% of the hours when RH 

exceeds 60% occur when the A/C is barely running (0–0.1 run time fraction).

Figure 4: Number of Hours > 60% RH Based on A/C Run Time Fraction

Figures 5 and 6 show the average daily profiles for the space sensible cooling load 

and latent load for April. The space sensible load follows the expected trend with a peak 

in mid- to late afternoon. The sharp peak at 6 A.M. in the space latent load is due to the 

bathroom exhaust ventilation. For April the average latent load for the high-performance 

home is approximately 42% lower than for the reference home compared to an average 

reduction of 35% in the sensible cooling load. Because of a much tighter building 

envelope and despite whole-house mechanical ventilation, the latent load for the highperformance home was reduced by a greater percentage than the sensible cooling load 

compared to the reference home. Thus, the current analysis shows humidity problems are 

not necessarily unique to high-performance homes.

Figure 5: Space Sensible Cooling Load Average Daily Profile for April

0

200

400

600

800

1000

0-0.1 0.1-0.2 0.2-0.3 0.3-0.4 0.4-0.5 0.5-0.6 0.6-0.7 0.7-0.8 0.8-0.9 0.9-1

Number of Hours > 60% RH

A/C Run Time Fraction

Reference Home IECC 2006 Home High Performance Home - A/C Only (Case 0)

0

4000

8000

12000

16000

20000

0

1000

2000

3000

4000

5000

6000

0 2 4 6 8 10 12 14 16 18 20 22 24

Space Sensible Cooling Load (Btu/hr)

Space Sensible Cooling Load (W)

Hour of Day

Reference Home 2006 IECC Home High Performance Home
11

Figure 6: Space Latent Load Average Daily Profile for April

Predictions of Thermal Comfort

EnergyPlus offers three thermal comfort models: Fanger (Fanger 1970), Pierce 2-

node (Gagge et al. 1986) and KSU 2-node (Azer and Hsu 1977). Similar thermal comfort 

trends with respect to space temperature and RH were observed in all three models. 

Results displayed in Table 6 are Fanger Predicted Mean Vote (PMV) results only. A 

clothing (clo) schedule was created to take into account seasonal variation: December 

through February, clo = 1.0; March through April and October through November, clo = 

0.75; May through September, clo = 0.5. 

Table 6: Thermal Comfort Analysis (based on Fanger PMV)

Case Description Maximum PMV 

Value

Hours Exceeding

PMV = +0.5

– Reference Home 0.95 718

– 2006 IECC Home 0.79 306

0 A/C Only 0.66 121

1 Thermostat Reset 0.57 23

2 A/C w/ ERV 0.65 134

3 HX Assisted A/C 0.64 109

4 A/C w/Condenser Reheat 0.56 28

5 A/C w/Desiccant Wheel Dehumidifier 0.58 71

6.1 A/C w/Small High-Efficiency Dehumidifier 0.61 112

6.2 A/C w/Medium High-Efficiency Dehumidifier 0.61 110

6.3 A/C w/Large High-Efficiency Dehumidifier 0.61 111

7 A/C w/Standard-Efficiency Dehumidifier 0.61 114

8 A/C w/ERV and Small High-Efficiency Dehumidifier 0.61 119

9 A/C w/ERV and Standard-Efficiency Dehumidifier 0.61 120

Note: Cases 4 –9 PMV are examined for RH set point of 55% only.

Table 6 displays the maximum PMV value and total number of hours exceeding a 

PMV of +0.5. Trends in maximum PMV values and total hours exceeding a +0.5 PMV 

do not correlate to the trends in RH presented in Tables 3 and 4.

Figure 7 examines the Fanger PMV trend for a space with uniform temperature (mean 

radiant temperature = air temperature), human metabolic rate of 1.0, clo 1.0, and air 

velocity 19.7 ft/min (0.1 m/s). The relatively low slopes of the PMV bands with respect 

0

400

800

1200

1600

2000

0

100

200

300

400

500

600

700

0 2 4 6 8 10 12 14 16 18 20 22 24

Space Latent Load (Btu/hr)

Space Latent Load (W)

Hour of Day

Reference Home 2006 IECC Home High Performance Home
12

to RH show the insensitivity of Fanger PMV to space RH change. It is also calculated 

that a 10% increase in RH results in the same amount of increase in Fanger PMV as a 

0.5°F (0.26°C) increase of air temperature, given the above set conditions. Alternately

speaking, a 10% increase in RH is predicted to be offset by a drop in air temperature of 

0.5°F (0.26°C) (Fountain and Huizenga 1997).

Figure 7: Fanger PMV Trend With Respect to Relative Humidity and Temperature

Figure 8 displays the ASHRAE Standard 55 (ASHRAE 2004b) thermal comfort 

regions for 80% of the occupants to be satisfied. The thermal comfort regions extend over 

a fairly large range in RH compared to temperature, meaning humans are less sensitive to 

humidity than to temperature. The comfort regions also set an upper limit of humidity 

ratio at 0.012 kg/kg dry air. With the modeled thermostat set points, the hours when PMV 

exceeds +0.5 are essentially equivalent to space humidity ratio exceeding 0.012 kg/kg dry 

air, unless clo or metabolic rate exceeds the range in Standard 55, where skin sweating 

regulation fails (ASHRAE 2009a). This indicates that an occupant is unlikely to notice 

the humidity problem in a home from a thermal comfort standpoint. Despite the variation 

of hours exceeding a PMV of 0.5 in the high-performance home, the PMV exceeds a 

value of +0.5 for less than 1.4% of the year for all the cases.

21.5

22

22.5

23

23.5

24

24.5

25

45 50 55 60 65 70 75 80

Air and Mean Radiant Temperature (°C)

Relative Humidity (%)

0.9-1

0.8-0.9

0.7-0.8

0.6-0.7

0.5-0.6

0.4-0.5

0.3-0.4

0.2-0.3

0.1-0.2

0-0.1

-0.1-0

-0.2--0.1

-0.3--0.2

-0.4--0.3

70.7

71.6

72.5

73.4

74.3

75.2

76.1

77

Air and Mean Radiant Temperature (°F)
13

Figure 8: ASHRAE Standard 55 Range of Operative Temperature and Humidity

Energy Consumption Summary 

Tables 7 and 8 show the annual source energy consumption for the reference home, 

the IECC 2006 home, and the high-performance home for all the parametric cases. 

Source-to-site conversion ratios are 3.365 for electricity and 1.092 for natural gas (Deru 

and Torcellini 2007).

Table 7: Source Energy Consumption Summary for Parametric Cases 

MBtu/yr (GJ/yr)

Case Description

Misc.

+ 

Large 

Appl. Lights

Hot 

Water

Vent 

Fans Cooling Heating

H/C 

Fan Total

– Reference 

Home

68.0 

(71.8)

30.9 

(32.6)

18.3 

(19.3)

0.3

(0.3)

93.1 

(98.2)

29.9 

(31.5)

29.6 

(31.6)

270.1 

(285.0)

– 2006 IECC 

Home

68.1 

(71.8)

30.9 

(32.6)

15.9 

(16.8)

2.8

(2.9)

59.9 

(63.2)

28.1

(26.6)

12.1 

(12.8)

216.4 

(228.3)

0 A/C Only 62.9 

(66.4)

8.6

(9.1)

9.3

(9.9)

1.8

(2.0)

29.4 

(31.0)

8.9

(8.4)

3.7

(3.9)

124.2 

(131.1)

1 Thermostat 

Reset

62.9 

(66.4)

8.6

(9.1)

9.3

(9.9)

1.8

(2.0)

33.3 

(35.1)

8.6

(9.1)

4.1

(4.3)

128.7

(135.8)

2 A/C w/ERV 62.9 

(66.4)

8.6

(9.1)

9.3

(9.9)

4.3

(4.5)

28.8 

(30.4)

7.3

(7.7)

3.5

(3.7)

124.7 

(131.6)

3 HX Assisted 

A/C

62.9 

(66.4)

8.6

(9.1)

9.3

(9.9)

1.8

(2.0)

32.9 

(34.7)

8.5

(8.9)

4.1

(4.3)

128.2 

(135.3)

0.000

0.002

0.004

0.006

0.008

0.010

0.012

0.014

0.016

50 59 68 77 86 95

10 15 20 25 30 35

Humidity Ratio (kg/kg dry air)

Operative Temperature (°F)

Operative Temperature (oC)

60% RH

20% RH

40% RH

80% RH

MET 1.0 - 1.3

Vel <= 0.2 m/s

1.0 clo

0.5 clo
14

Adding explicit humidity control equipment (Cases 4–9) increases whole-house 

source energy consumption (Table 8). Table 8 and Figure 9 indicate the same trend: an 

RH set point of 50% results in much more energy consumption than an RH set point of 

60%. Table 10 indicates that an RH set point of 50% results in increased run time for 

both the dehumidifier and the A/C compared to an RH set point of 60%, except for A/C 

with desiccant wheel dehumidifier (Case 5). In A/C w/ condenser reheat (Case 4), the 

A/C run time includes the dehumification run time because the A/C operates during both 

the cooling and the dehumidification modes. 

Table 8: Source Energy Consumption Summary for Active Dehumidification Parametric

Cases MBtu/Yr (GJ/Yr)

Case Description

Cooling and

Dehumidification Total* Total Percent Increasevs. Case 0

50% 55% 60% 50% 55% 60% 50% 55% 60%

4 A/C w/Condenser 

Reheat

54.0

(57.0)

39.0

(41.1)

32.3

(34.1)

152.0 

(160.4)

135.0 

(142.4)

127.4 

(134.4) 22.4% 8.7% 2.6%

5

A/C w/Desiccant 

Wheel 

Dehumidifier

40.7

(42.9)

34.3

(36.2)

30.6

(32.3)

141.2 

(149.0)

131.6 

(138.8)

126.0 

(133.0) 13.7% 5.9% 1.5%

6.1

A/C w/Small HighEfficiency

Dehumidifier

53.5

(56.4)

39.3

(41.5)

32.5

(34.3)

148.2 

(156.4)

133.9 

(141.3)

127.1 

(134.1) 19.3% 7.8% 2.3%

6.2

A/C w/Medium

High-Efficiency 

Dehumidifier

50.3

(53.1)

38.1

(40.2)

32.2

(34.0)

145.0 

(153.0)

132.8 

(140.1)

126.9 

(133.9) 16.7% 6.9% 2.2%

6.3

A/C w/Large HighEfficiency 

Dehumidifier

45.3

(47.7)

36.4

(38.4)

32.0

(33.7)

139.9 

(147.6)

131.0 

(138.2)

126.6 

(133.6) 12.7% 5.5% 1.9%

7

A/C w/StandardEfficiency 

Dehumidifier

60.8

(64.1)

41.7

(44.0)

32.9

(34.7)

155.5 

(164.1)

136.4 

(143.9)

127.5 

(134.5) 25.2% 9.8% 2.7%

8

A/C w/ERV and

Small HighEfficiency 

Dehumidifier

44.3

(46.7)

33.7

(35.5)

30.7

(32.4)

147.5

(139.8)

129.3 

(136.4)

126.4 

(133.4) 12.6% 4.1% 1.8%

9

A/C w/ERV and

Standard-Efficiency 

Dehumidifier

48.9 

(51.6)

34.7 

(36.6)

32.7

(31.0)

144.5 

(152.4)

130.3 

(137.5)

126.7 

(133.7) 16.3% 4.9% 2.0%

* Total column is the summation of all end uses: miscellaneous and large appliances, lights, hot water, ventilation fans, heating, cooling and 

dehumidification, heating and cooling fans.
15

Figure 9: High-Performance Home Percent Increase of Whole-House Energy Consumption vs. 

Case 0

Table 9: A/C and Dehumidifier Run Time Comparison

Case Description

A/C Run Time

(h)

Dehumidifier Run Time

(h)

– BA Benchmark Home 2,204 0

– 2006 IECC Home 2,068 0

0 A/C Only 1,674 0

1 Thermostat Reset 1,912 0

2 A/C w/ERV 1,647 0

3 HX-Assisted A/C 1,910 0

Table 10: A/C and Dehumidifier Run Time Comparison

Case Description

A/C Run Time 

(h)

Dehumidifier Run Time 

(h)

50% 55% 60% 50% 55% 60%

4 A/C w/Condenser Reheat 3,356 2,307 1,844 1,785 628 139

5 A/C w/Desiccant Wheel Dehumidifier 1,467 1,591 1,659 2,344 1,018 241

6.1 A/C w/Small High-Efficiency Dehumidifier 2,006 1,803 1,701 2,447 948 225

6.2 A/C w/Medium High-Efficiency Dehumidifier 1,979 1,794 1,700 1,854 720 174

6.3 A/C w/Large High-Efficiency Dehumidifier 1,931 1,782 1,701 1,180 471 123

7 A/C w/Standard-Efficiency Dehumidifier 2,075 1,825 1,704 2,745 1,014 231

8 A/C w/ERV and Small High-Efficiency

Dehumidifier 1,846 1,695 1,654 1,563 431 112

9 A/C w/ERV and Standard-Efficiency 

Dehumidifier 1,889 1,703 1,655 1,757 462 117

The percent increase of source energy consumption (see Figure 9) is the required 

energy penalty of achieving home durability and maintaining healthy indoor air quality. 

A few observations were made:

• In the high-performance home with explicit dehumidification control (Cases 4–9),

using a 50% RH set point increased the whole-house energy consumption by 12.6%–

0%

5%

10%

15%

20%

25%

30%

Case 1Case 2Case 3Case 4Case 5

Case 6.1Case 6.2Case 6.3

Case 7Case 8Case 9

No Active Control 50% RH 55% RH 60% RH

Whole House Energy Consumption 

Percent Increase vs. Case 0
16

22.4%; a 60% RH set point increased the whole-house energy consumption by only

1.5%–2.7%.

• Using an RH set point of 60% significantly reduced the dehumidifier or A/C 

dehumidification mode run time (Cases 4–9) as opposed to using RH set points of

50% and 55%. This in turn reduces the A/C run time, except for Case 5.

• Among all the active dehumidification technologies, A/C with desiccant wheel 

dehumidifier (Case 5) is the only option that reduced A/C run time. The desiccant 

wheel dehumidifier supplies cool air, so the A/C load is partially offset during 

dehumidifier operation. A/C with standard-efficiency DX dehumidifier (Case 7) 

showed the highest percent increase in the whole-house source energy consumption. 

• Among the three dehumidifiers (Cases 6.1, 6.2, and 6.3), the most efficient and 

largest capacity (Case 6.3) resulted in the lowest energy consumption compared to the 

smaller dehumidifiers, despite more part-load losses.

CONCLUSION

EnergyPlus modeling results with RH excursion analysis showed that all three homes 

(mid-1990s reference home, IECC 2006 home, and high-performance home) are prone to 

mold growth from long excursions of uncontrolled high humidity. Humidity problems are 

not unique to the high-performance home in the hot-humid climate compared to the mid1990s reference home or the IECC 2006 home. Thermal comfort analysis indicates that 

occupants are unlikely to feel the humidity problems in a home; thus, humidy can pose a 

risk to home durability and health.

Adding active humidity control equipment (Cases 4–9) effectively controls RH to a 

safe level in the high-performance home. The 50% RH set point results in a significant

source energy consumption penalty (12.6%–22.4% increase vs. Case 0) compared to the

60% set point (1.5%–2.7% increase vs. Case 0). At RH set points of 50% and 55%, A/C 

with desiccant wheel dehumidifier (Case 5) and A/C with ERV and high-efficiency DX 

dehumidifier (Case 8) stand out as the two options resulting in the smallest increase of 

source energy consumption. At an RH set point of 60%, all explicit dehumidification 

technologies (Cases 4–9) result in similar insignificant increases in source energy 

consumption and thus are equally competitive. Other factors such as cost, system 

configuration and complexity, and maintenance would therefore be dominant in 

determining which strategy to employ.

The study has several limititations:

• It is limited to Houston. Other cities in the hot-humid climate and cities in the mixedhumid climate can result in different indoor humidity levels.

• House internal operating conditions such as moisture generation rates and space 

temperature set points can vary significantly from house to house, and thus can lead 

to different levels of humidity in individual houses. 

• Building envelope interactions with indoor and outdoor air humidity conditions are 

not analyzed. The moisture buffering behavior of building materials and furnishings 

was assumed to be constant and was modeled as a lumped capacitance.
17

REFERENCES

Anderson, R., and D. Roberts. 2008. Maximizing residential energy savings: net zero 

energy house (ZEH) technology pathways. Report NREL/TP-550-44547, National 

Renewable Energy Laboratory, USA.

ASHRAE. 2004a. ANSI/ASHRAE Standard 62.2-2004, Ventilation and Acceptable 

Indoor Air Quality in Low-Rise Residential Buildings. Atlanta: American Society of 

Heating, Refrigerating and Air-Conditioning Engineers, Inc.

ASHRAE. 2004b. ANSI/ASHRAE Standard 55-2004, Thermal Environmental Conditions 

for Human Occupancy. Atlanta: American Society of Heating, Refrigerating and Air- Conditioning Engineers, Inc.

ASHRAE. 2009a. 2009 ASHRAE Handbook—Fundamentals. Atlanta: American Society 

of Heating, Refrigerating and Air-Conditioning Engineers, Inc.

ASHRAE. 2009b. ANSI/ASHRAE Standard 160-2009, Criteria for Moisture-Control 

Design Analysis in Buildings. Atlanta: American Society of Heating, Refrigerating 

and Air-Conditioning Engineers, Inc.

Azer, N.Z., and S. Hsu. 1977. The prediction of thermal sensation from simple model of 

human physiological regulatory response. ASHRAE Transactions 83(1).

Christensen, D., and J. Winkler. 2009. Laboratory test report for ThermaStor Ultra-Aire 

XT150H dehumidifier. Report NREL/TP-550-47215, National Renewable Energy 

Laboratory, USA.

DOE. 2010. EnergyPlus version 6.0. U.S. Department of Energy.

Deru, M., and P. Torcellini. 2007. Source energy and emission factors for energy use in 

buildings. Report NREL/TP-550-38617, National Renewable Energy Laboratory, 

USA.

Emmerich, S., C. Howard-Reed, and A. Gupte. 2005. Modeling the IAQ impact of HHI 

interventions in inner-city housing. NISTR 7212, National Institute of Standards and 

Technology, USA. EPA. 2001. Indoor Humidity Assessment Tool (IHAT) Reference Manual.

EPA. 2010. A Brief Guide to Mold, Moisture and Your Home, www.epa.gov/mold.

Fanger, P.O. 1970. Thermal comfort: Analysis and applications in environmental 

engineering. Danish Technical Press, Copenhagen, Denmark.

Fountain, M., and C. Huizenga. 1997. A thermal sensation prediction software tool for 

use by the profession. ASHRAE Transactions 103(2).

Gagge, A.P., AP. Fobelets, and L.B. Berglund. 1986. An effective temperature scale 

based on a simple model of human physiological regulatory response. ASHRAE 

Transactions 92(2).

Henderson, H., K. Rengarajan, and D. Shirey III. 1992. The impact of comfort control on 

air conditioner energy use in humid climates. ASHRAE Transactions 98(2):104-13.

Henderson, H., D. Shirey, and C.K. Rice. 2008. Can conventional cooling equipment 

meet dehumidification needs for houses in humid climates? 2008 ACEEE Summer 

Study on Energy Efficiency in Buildings, Pacific Grove, CA.

Henderson, H., with CDH Energy Corp., Cazenovia, NY. Email exchange with author, 

October 19, 2010.

Hendron, R., and C. Engebrecht. 2010. Building America research definition: Updated 

December 2009. Report NREL/TP-550-47246, National Renewable Energy 

Laboratory, USA.

ICC. 2006. International Energy Conservation Code.

Lstiburek, J.W. 1993. Humidity control in the humid south. Building Enclosure 

Technology and Environmental Council Workshop Proceedings. 

Occupational and Environmental Epidemiology. 2005. Mold and human health. 

Occupational and Environmental Epidemiology, North Carolina Department of 

Health and Human Services, Division of Public Health, NC, USA.
18

Rudd, A., and H.I. Henderson. 2007. Monitored indoor moisture and temperature 

conditions in humid-climate US residences. ASHRAE Transactions 113(1): 435-49.

Tenwolde, A., and I. Walker. 2001. Interior moisture design loads for residences. 

Buildings VIII: Performance of exterior envelopes of whole buildings, Clearwater 

Beach, FL, USA. Walker, I., and D. Wilson. 1998. Field validation of algebraic equations for stack and 

wind driven air infiltration calculations. International Journal of HVAC&R Research

4(2).

Walker, I., and M. Sherman. 2007. Humidity implications for meeting residential 

ventilation requirements. Report LBNL-62182, Earnest Orlando Lawrence Berkeley 

National Laboratory, USA. 
F1147-E(10/2008) 

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4. TITLE AND SUBTITLE

Using EnergyPlus to Perform Dehumidification Analysis on Building 

America Homes: Preprint

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14. ABSTRACT (Maximum 200 Words)

A parametric study was conducted using EnergyPlus version 6.0 to investigate humidity issues on a typical mid1990s reference home, a 2006 International Energy Conservation Code home, and a high-performance home in a 

hot-humid climate. The impacts of various dehumidification equipment and controls are analyzed on the high 

performance home. The study examined the combined effects of infiltration and mechanical ventilation with balanced 

and unbalanced mechanical ventilation systems. Indoor relative humidity excursions were examined; specifically, the 

number of excursions, average excursion length, and maximum excursion length. Space relative humidity, thermal 

comfort, and whole-house source energy consumption were analyzed for indoor relative humidity set points of 50%, 

55%, and 60%. The study showed and explained why similar trends of high humidity were observed in all three 

homes regardless of energy efficiency, and why humidity problems are not necessarily unique in high-performance 

homes. Thermal comfort analysis indicated that occupants are unlikely to notice indoor humidity problems. The study 

confirmed that supplemental dehumidification should be provided to maintain space relative humidity below 60% in a 

hot-humid climate. 

15. SUBJECT TERMS

dehumidification; energyplus; relative humidity; infiltration; mechanical ventilation

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