Field Test Protocol: Standard 

Internal Load Generation for 

Unoccupied Test Homes 

X. Fang and D. Christensen 

National Renewable Energy Laboratory

G. Barker and E. Hancock 

Mountain Energy Partnership

June 2011
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Field Test Protocol: Standard Internal Load Generation for 

Unoccupied Test Homes

Prepared for: 

Building America

Building Technologies Program

Office of Energy Efficiency and Renewable Energy 

U.S. Department of Energy 

Prepared by: 

Advanced Residential Buildings Group 

Electricity, Resources & Building System Integration

National Renewable Energy Laboratory 

1617 Cole Blvd, 

Golden, CO 

June 2011 
ii

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iii

Contents

List of Figures ............................................................................................................................................ iii

List of Tables .............................................................................................................................................. iii

Definitions ................................................................................................................................................... iv

Introduction ................................................................................................................................................. 1

Load Calculation ......................................................................................................................................... 2

Compliance With HSP ...............................................................................................................2

Different Loads in Different Spaces ..........................................................................................2

Load Generation.......................................................................................................................................... 5

Load-Generating Equipment ......................................................................................................5

Sensible Load Generation ....................................................................................................5

Latent Load Generation .......................................................................................................5

References................................................................................................................................................... 9

List of Figures

Figure 1. Kitchen humidifier in a laboratory home.................................................................................. 7

Figure 2. Humidifier piping diagram and controls................................................................................... 7

List of Tables

Table 1. Sample Internal Sensible and Latent Load Profile.................................................................... 3

Table 2. Sample Internal Sensible and Latent Profiles for Individual Bedrooms................................. 4

Table 3. List of Heaters and Humidifiers .................................................................................................. 5

Table 4. List of Instrumentation................................................................................................................. 6

Table 5. Room Heaters and Humidifiers................................................................................................... 8

Table 6. Load Profiles With Sensible Load Adjusted .............................................................................. 8
iv

Definitions

BA Building America

DC Direct Current

HSP House Simulation Protocol

NC Normally Closed
1 

Introduction

In Building America prototypical homes, it is common to conduct heavily instrumented shortterm tests (which are akin to a research-level commissioning exercise) prior to occupancy. These 

tests are used primarily to ensure each home is built to specification, and that the systems are 

operating as the manufacturers intended. Once a home is occupied, lower level instrumentation is 

typically used for long-term monitoring of its systems to gauge whether the home and systems 

achieve the expected energy performance in a real-world setting. Instrumentation is reduced 

during occupied, long-term monitoring because: 

• Heavy instrumentation may inconvenience occupants. 

• Monitoring complex real-time occupant behaviors is difficult because they do not lend 

themselves to consistent prediction or modeling. 

• Occupant behaviors represent only the study household, and are unlikely to be average or 

standard. Many times we want to observe occupancy stressing a home by operating it in 

unexpected ways, but capturing that and translating it back to simulation are extremely 

difficult. This often makes it difficult to demonstrate energy savings in a statistically 

relevant way.

One way to investigate a subset of occupant-incurred impacts is to use unoccupied homes and 

create heat and moisture loads to represent “standard” occupants. This forces building systems to 

operate with realistic but known loads, and eliminates the complexity and uncertainty created by 

occupant behaviors during long-term monitoring. When the loads generated during the field test 

align with loads used to simulate the building, determining that the building was constructed as 

specified and that equipment is operating as designed becomes much more straightforward.

A few researchers have tried to generate representative loads, but those efforts were generally 

not consistent with the Building America House Simulation Protocol (HSP) (Hendron and 

Engebrecht 2010). The most recent effort was by Oak Ridge National Laboratory with real-time 

automated control of lights and appliances as well as human load simulation in heavily 

instrumented field laboratory houses (Christian et al. 2010). The load generation complies with 

HSP, but the heavy instrumentation was expensive and required intensive custom engineering 

effort. 

This report describes a simple and general way to generate HSP-consistent internal sensible and 

latent loads in unoccupied homes. It is newly updated and provides instructions about how to 

calculate and set up the operational profiles in unoccupied homes. The document is split into two 

sections: how to determine the internal loads’ magnitudes and schedules, and which tools and 

methods should be used to generate those internal loads to achieve research goals. 
2 

Load Calculation

Compliance With HSP

HSP prescribes the annual energy or usage consumption calculation methods for lighting, 

appliances, miscellaneous electric and gas loads, and domestic hot water, with individual 

normalized hourly profiles for each. HSP also prescribes occupancy profiles with average 

sensible and latent hourly loads. To determine internal loads complying with HSP, a researcher 

should use Building America (BA) analysis spreadsheets on “New Construction” or “Existing 

Home” (Building America 2011). These provide annual hourly operational profiles for each end 

use. End uses that the researcher plans to study and control individually (for example, lighting 

and lighting controls) should be drawn from the appropriate analysis spreadsheet. All other end 

use loads, when summed together, become the whole-house sensible and latent load hourly 

profiles, which can be generated using this protocol. 

Different Loads in Different Spaces

Generating a central artificial latent and sensible load to match the HSP profile usually suffices 

for a whole-house simulation need. In field test settings the load generators may need to be 

distributed to effectively replicate loads that would occur in individual spaces of interest. And if 

the central location is in a confined space, the researcher may not achieve the expected load. 

How to best distribute the load generators, and what level of load divisions are required, depend 

heavily on the research questions being addressed in that test home. For example, if the air 

handler is of primary interest to the study and local condensation is not a concern, a point source 

for the whole house or one for each floor may very well suffice. On the other hand, if air 

distribution and thermal comfort in upstairs bedrooms are of particular concern, distributed loads 

may be appropriate. But for the latter scenario, logistical concerns such as frequency of refilling 

humidifiers and spillage possibility for hard-plumbed humidifiers will need to be addressed 

carefully.

Table 1 is an example of a weekday profile of occupantgenerated space loads, based on the 2010 HSP profiles, for a 

3,300-ft2, 4-bedroom, 2.5-bath, 2-story home with a finished 

basement. Sensible and latent loads are divided into 

downstairs and upstairs portions. Basement load is grouped 

into the downstairs (first floor) portion. Appliances such as 

the clothes washer, clothes dryer, dishwasher, refrigerator, 

cooking range, and oven are grouped with downstairs loads. 

Lighting, miscellaneous electric loads, and sink uses are split 

into downstairs and upstairs portions. Shower and bath loads 

are put into the upstairs portion. Downstairs (living space) 

and upstairs (bedroom space) occupancy profiles are used 

based on HSP. Volume of moisture is calculated based on 

latent heat of vaporization (hfg) for water at room temperature 

70°F (21.1°C), i.e. hfg = 1075 Btu/lbm (2500 J/g). For water 

density, 62.32 lbm/ft3 (1 g/mL) is assumed. Note that if the 

test home has a refrigerator, it should be unplugged during 

the test period so that sensible load is not duplicated. 

Example: Generating the 

whole-house latent load in 

a bathroom shower stall 

without distributed air 

circulation will impose too 

heavy a local moisture load 

and cause local air 

saturation and 

condensation on surfaces. 

This will shift the latent-tosensible load ratio and 

delay the release of latent 

load of interest (change in 

schedule). Further, the 

moisture may be absorbed 

into building materials or 

run down the drain instead 

of being removed by 

mechanical equipment.
3 

Table 1. Sample Internal Sensible and Latent Load Profile

Hour

Downstairs/Living Upstairs/Bedrooms

Sensible 

(Wh)

Latent 

(Wh)

Moisture 

(mL)

Sensible 

(Wh)

Latent 

(Wh)

Moisture 

(mL)

1 168 15 21 314 147 217

2 158 13 19 304 143 211

3 150 10 15 301 142 209

4 148 10 15 301 143 211

5 171 12 17 327 147 217

6 227 15 23 402 169 248

7 382 117 173 370 140 206

8 408 132 195 337 119 176

9 338 114 169 198 62 91

10 295 91 134 161 50 73

11 294 89 131 153 42 61

12 297 92 136 143 35 51

13 297 94 139 133 28 41

14 289 88 130 131 25 37

15 287 86 127 133 23 34

16 316 92 136 156 24 36

17 417 120 176 226 28 42

18 570 192 283 291 36 53

19 686 241 355 354 39 58

20 688 215 317 395 39 58

21 675 202 298 402 39 57

22 625 219 323 329 38 55

23 415 120 177 338 95 141

24 221 21 31 365 155 228

Total 8519 2402 3539 6565 1908 2811

If room thermal comfort and air distribution are of particular research concern to a researcher,

such as in bedrooms and bathrooms, load generation can be further split for each bedroom and 

bathroom. 

Table 2 is an example of subdividing the loads into master bedroom, master bathroom, and two 

of the three guest bedrooms. Shower, bath, and sink are all grouped into the master bathroom. 

Lighting, miscellaneous, and occupancy loads are evenly divided into each simulated bedroom.
4 

Table 2. Sample Internal Sensible and Latent Profiles for Individual Bedrooms

Hour

Downstairs/Living Each Bedroom (3 total) Master Bathroom

Sensible 

(Wh)

Latent 

(Wh)

Moisture 

(mL)

Sensible 

(Wh)

Latent 

(Wh)

Moisture 

(mL)

Sensible 

(Wh)

Latent

(Wh)

Moisture 

(mL)

1 168 15 21 93 44 65 35 15 22

2 158 13 19 92 44 65 29 11 16

3 150 10 15 91 44 65 27 10 14

4 148 10 15 91 44 65 28 11 15

5 171 12 17 96 44 65 39 15 22

6 227 15 23 109 44 65 76 36 53

7 382 117 173 82 22 33 126 73 108

8 408 132 195 70 15 22 128 74 110

9 338 114 169 32 0 0 103 62 91

10 295 91 134 26 0 0 84 50 73

11 294 89 131 26 0 0 73 42 61

12 297 92 136 26 0 0 64 35 51

13 297 94 139 26 0 0 55 28 41

14 289 88 130 26 0 0 52 25 37

15 287 86 127 28 0 0 50 23 34

16 316 92 136 33 0 0 57 24 36

17 417 120 176 49 0 0 78 28 42

18 570 192 283 64 0 0 100 36 53

19 686 241 355 77 0 0 122 39 58

20 688 215 317 87 0 0 135 39 58

21 675 202 298 89 0 0 135 39 57

22 625 219 323 72 0 0 113 38 55

23 415 120 177 85 22 33 83 29 43

24 221 21 31 103 44 65 57 23 33

Total 8519 2402 3539 1572 368 542 1850 803 1184
5 

Load Generation

Load-Generating Equipment

Two loads are being generated: sensible and latent. 

Sensible Load Generation

Electric convective heaters should be used to generate sensible load. These heaters contain a 

resistance heating element and a fan. This equipment was chosen because of the added benefit of 

circulating the load for more realistic temperature distribution. The heater must be oriented so 

that fan-forced convection does not affect other systems. For example, if the heater blows 

directly at a large sliding glass door, the home envelope heat transfer will be undesirably altered. 

Proximity of the heater to sensors also needs to be considered. 

Each heater should have its power cord metered; electrical energy consumed is equal to sensible 

load generated. Heaters and humidifiers shall be cycled on at the start of every 15-minute 

timestep, for sufficient duration to generate the desired hourly profile. Once 25% of the hourly 

load is reached from power metering feedbacks (in kilowatt-hours), the heater should be cycled 

off for that timestep. It is desirable to have long runtimes, so the heater should be sized as closely 

as possible to the highest hourly load. 

Latent Load Generation

An ultrasonic humidifier, which uses a metal diaphragm vibrating at an ultrasonic frequency to 

create very fine water droplets that silently exit the humidifier as cool fog, should be used to 

generate latent load. Unlike a steam humidifier, it can release moisture at room temperature 

almost instantly without a warmup period, and does not heat the room air with hot steam from a 

heated water basin. And unlike an evaporative humidifier, its moisture release rate is steady 

regardless of ambient relative humidity. Therefore, using an ultrasonic humidifier is a more 

effective way of dividing sensible and latent into separately controllable loads. Demineralization 

cartridges and regular cleaning are required to prevent mineral buildup. The humidifier should 

face toward the center of the room to allow water droplets to fully evaporate. The humidifier 

may need to be elevated so the atomized water can evaporate before it lands on a solid surface 

such as a floor or cabinet.

The humidifier’s water reservoir will not hold sufficient water for long-term monitoring. The 

water level can be maintained manually or automatically. For a manual refill operation, the 

researcher will need to calculate the moisture release rate, humidifier container volume, daily 

loads, and number of days between refills to determine the number of humidifiers needed. A 

schematic for automatic reservoir filling is provided in Figure 1. Table 3 shows a list of heaters 

and humidifiers needed to generate the load profiles in Table 1. 

Table 4 provides a list of instrumentation that enables automated load generation. This list is for 

reference only, but is representative of a test home’s requirements. 
6 

Table 3. List of Heaters and Humidifiers

Equipment Location Manufacturer/Model Capacity Electrical Accessories Comment

Electric heater Center of 

family room

Sunbeam SFH1000 1,200 W 120 V, 1200 W None A 

Humidifier Kitchen

counter, 

next to sink

Sharper Image 

HE100283

5.72 mL/min 

(lab tested)

120 V, 45 W AOS 7531 

demineralization 

cartridge

B

Electric heater Upstairs 

hallway

Sunbeam SFH1000 1,200 W 120 V, 1200 W None A

Comments: 

A Heat/fan only setting. 

B Provide water mineral filter at sink faucet to reduce mineralization. PUR, GE, or equivalent filters are acceptable.

Table 4. List of Instrumentation

Monitored / 

Controlled 

Parameter

Sensor Description Sensor 

Manufacturer

Sensor Part 

Number

Sensor 

Accuracy Qty. Comment

For Humidifier

Make-up water 

flow rate

Plastic flow sensor: low to 

medium water flow rate 

Omega FTB601B ± 1% of 

reading

1

Control valve 2-way N.C. solenoid valve 

for potable water

ASCO 8256 NSF 61-1/4” NA 1 A

Level switch Ultrasonic solid-state 

liquid level switch

Omega LVU-A701 NA 1 B

AC/DC relay 

controller with 

manual override

Humidifier power 

disconnect and make-up 

water control valve relay

Campbell SDM-CD16AC NA 1 C 

Humidifier power 

disconnect 

Solid-state relay Grainger 1EGJ5 NA 1 

Humidifier makeup water control 

valve relay 

Solid-state relay Grainger 1EGJ5 NA 1

Humidifier current Current transducer with 

0–5-V DC output

LEM AT 10 B5 ± 1.5% 1 D

For Electric Heater

AC/DC relay 

controller with 

manual override

Heater power disconnect Campbell SDM-CD16AC NA 1 C

Solid-state relay Power disconnect Grainger 1EGJ5 NA 1

Electric heater Watt node power meter Continental 

Control 

Systems 

WNB-3Y-208-P3 

100HZ output

± 0.5% 1

Solid core current 

transformer

Continental 

Control 

Systems

CTS-0750-015 ± 1% 1

General Note: use 3/8-in. copper pipe, braided flex stainless steel metal piping or 1/4-in. PVC piping rated at 100 psig minimum, 

with compression fittings to plumb supply water to the flow meter, solenoid valves, and humidifier. 

Comments: 

A N. C. Normally closed, power open. Solenoid valve will close on losing power. 

B Normally open level switch by default. When the high water level is reached or the level switch loses power, the level switch will 

disconnect power to the solenoid valve. 

C Only a control point is needed on the relay controller. 

D When two or three manual refill humidifiers are bundled together in parallel operations, one current transducer can be used to 

meter the total lumped power. 
7 

Figure 1 shows a photo of the plumbed humidifier with flow meter and solenoid valve under the 

kitchen faucet in a pilot test home. The humidifier has two water basins. The top tanks were 

removed to enable auto feed application. Two acrylic plates with precut holes were glued to the 

rim of the water basins. The plates cover the water surface with holes for make-up water line and 

level switch. An electrical bushing (a hollow insulating liner) was used to support the level 

switch. A push-in fitting was used to support the make-up water tubing. The level switch and the 

make-up water inlet were purposely placed on different sides of the humidifier. This gave some 

room for water self leveling in the basins during every water feed and prevented unstable 

operation of the level switch. A demineralization cartridge needs to be placed in the same basin 

with the make-up water line to prevent unstable operation of the level switch. Figure 2 is a 

schematic of piping diagram with controls layout. 

 

Figure 1. Kitchen humidifier in a laboratory home

Figure 2. Humidifier piping diagram and controls NREL/PIX 19201 Credit: Xia Fang

NREL/PIX 19202 Credit: Xia Fang

NREL/PIX 19203 Credit: Xia Fang
8 

At the beginning of each timestep, the solenoid valve for make-up water shall open for water 

feed to the humidifier until the level switch high level line is reached. The flow meter provides a 

reading and gives feedback for the make-up water provided. 

Alternately, for generating separate small room loads, small convective heaters and manual feed 

humidifiers can be used. Table 5 shows the recommended small humidifiers and heaters for that 

situation.

Table 5. Room Heaters and Humidifiers

Equipment Location Manufacturer/Model Capacity Electrical Accessories Comments

Electric heater Bedroom Burton 150/300W 

ceramic heater and fan

150 W 120 V 12-V converter 

Humidifier Bedroom Sharper Image 

HE100280

4.75 

mL/min 

(Lab tested)

120 V,

25 W

Demineralization 

cartridge 

One-gallon tank. 

Humidifier shall 

have manual water 

feed once a week.

Ultrasonic humidification is almost load-neutral to the room air. While evaporation of water 

droplets creates a positive latent load, this results in a negative sensible (cooling) load. Power 

consumption of the humidifier only partly offsets the negative sensible load to the room air, so 

heater runtimes must be increased to compensate. Table 6 shows the necessary sensible load 

adjustment compared with Table 1, and represents the final control strategy for load generation.

Table 6. Sample Load Profiles With Sensible Load Adjusted

Hour

Downstairs / Living Each Bedroom (3 total) Master Bathroom

Latent 

(Wh)

Moisture 

(mL)

Adjusted 

Sensible 

(Wh)

Latent 

(Wh)

Moisture 

(mL)

Adjusted 

Sensible 

(Wh)

Latent 

(Wh)

Moisture 

(mL)

Adjusted 

Sensible 

(Wh)

1 15 21 179 44 65 129 15 22 47

2 13 19 168 44 65 127 11 16 38

3 10 15 158 44 65 127 10 14 35

4 10 15 156 44 65 127 11 15 37

5 12 17 180 44 65 132 15 22 51

6 15 23 240 44 65 144 36 53 105

7 117 173 477 22 33 99 73 108 185

8 132 195 515 15 22 82 74 110 188

9 114 169 430 0 0 32 62 91 152

10 91 134 368 0 0 26 50 73 124

11 89 131 366 0 0 26 42 61 107

12 92 136 372 0 0 26 35 51 92

13 94 139 373 0 0 26 28 41 78

14 88 130 360 0 0 26 25 37 72

15 86 127 356 0 0 28 23 34 69

16 92 136 390 0 0 33 24 36 76

17 120 176 513 0 0 49 28 42 101

18 192 283 725 0 0 64 36 53 129

19 241 355 880 0 0 77 39 58 154

20 215 317 862 0 0 87 39 58 167

21 202 298 838 0 0 89 39 57 167

22 219 323 802 0 0 72 38 55 143

23 120 177 511 22 33 103 29 43 107

24 21 31 238 44 65 138 23 33 75

Total 2402 3539 10457 368 542 1869 803 1184 2498
9 

References 

Building America Analysis Spreadsheets, companions to the House Simulation Protocol. 

www.eere.energy.gov/buildings/building_america/analysis_spreadsheets.html. January 2011. 

Christian, J.; Gehl, T.; Boudreaux, P.; New, J.; Dockery R. (2010). Tennessee Valley Authority’s 

Campbell Creek Energy Efficient Homes Project: 2010 First Year Performance Report, July 

1, 2009 – August 31, 2010. 

Hendron, R.; Engebrecht, C. (2010). Building America House Simulation Protocol: Updated 

October 2010. Golden, CO: National Renewable Energy Laboratory, NREL/TP-550-49246
DOE/GO-102011-3321 ▪ June 2011

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