Jan/feb 2011

$15

Dehumidifier Metering Study

Measured Performance of Energy-Efficient Homes

The Scary Crawl Space

Weatherization in Rural Alaska

EnERgy STAR 3.0 ▪ Tool REviEW—DigiTAl MAnoMETERS ▪ nREl’S BuilDing RESEARCH

44 Home Energy | Januar y/Februar y 2011

dehumidifier Metering Study

by anDy menDyk anD Dan cautley

Dehumidifier with “watts up” meter in wesh home. this dehumidifier was connected directly to a floor drain.

this dehumidifier was connected to a floor drain (drain not visible). A cap was taped onto the face of the meter to prevent accidental depression of meter reset button.

the black box located between this de-humidifier and watt’s up meter contained a line-status state logger that detects and measures the duration of interruptions in power to the dehumidifier.

Residential stand-alone dehumidifiers can draw a significant amount of power when in operation (power draws of 300–700 watts are common). However, little is known about the total seasonal energy use of dehu-

midifiers. Many factors can affect this total. Dehumidifier capacity, characteristics of the ambient space, and the homeowner’s selec-tion of set points are just some of the variables that determine how much energy a dehumidifier will ultimately consume. Wisconsin’s Focus on Energy recently commissioned a metering study to figure out just how much energy typical Wisconsin households use to dehumidify their homes.

The Energy Center of Wisconsin monitored dehumidifier use in 40 Wisconsin homes on behalf of Focus on Energy during a four-month period in the summer and fall of 2009 (see “Focus on Energy”). The sample of homes we monitored varied in age; it consisted of 20 newer (built since 2000) “Wisconsin Energy Star Homes (WESH) and 20 randomly selected homes. The ran-domly selected homes were located in one of three Wisconsin metropolitan areas (Milwaukee, Madison, and Eau Claire). The 20 WESH homes were located in Wisconsin’s Fox River Valley, in the east-central region of the state.

To add information about occupant use to our metered data, we randomly selected 43 WESH homes and surveyed their own-ers concerning their use of stand-alone dehumidifiers. We com-pared these survey results against 1,329 responses concerning dehumidifier use that were taken from our most recent Midwest Energy Survey (MES). (See “About the Midwest Energy Survey.”)

METERing RESUlTSWe metered several conditions in the 40 monitored homes. We used “Watts-up” watt-hour meters to collect watt-hours and watt-age (minimum, maximum, and average values) in five- to ten-minute increments over four months. We used Onset Computer’s Hobo U10 data loggers to monitor relative humidity (RH) and am-bient temperature in the main floor and in the basement of each home. The basement RH measurement loggers were placed near

44 Home Energy | Januar y/Februar y 2011

Focu

s on

energ

y

FoCus on EnErgy works with eligible Wisconsin resi-dents and businesses to install cost-effective energy efficiency and renewable energy projects. Focus information, resources, and financial incentives help to implement projects that other-wise would not be completed, or to complete projects sooner than scheduled. Its efforts help Wisconsin residents and busi-nesses manage rising energy costs, promote in-state economic development, protect our environment, and control the state’s growing demand for electricity and natural gas.

To learn more about Focus on Energy, go to www.focusonenergy.com.

www.homeenergy.org 45

the ceiling in the same room as, but not immediately adjacent to, the dehumidifiers. We used local hourly weather station data to estimate local outdoor temperature and RH.

For our study, we divided the monitoring period into two separate seasons. The summer season included data collected during July and August. The fall season included data collected during September and October. We found that on average, the dehumidifiers we metered used more energy during the sum-mer (6.5 kWh per day) than they used during the fall (4.8 kWh per day). The range in average dehumidifier energy use across all homes was significant; it ranged from a low value of 0 kWh per day to a high value of 17 kWh per day. During the summer, we found that the 20 newer WESH homes used an average of 1.6 kWh per day more than the non-WESH homes. We speculate that this difference in energy use is at least partially related to differences in the size of the houses; the median WESH home in our sample was 25% larger above grade and 93% larger below grade than the median non-WESH home.

We applied linear regression techniques to daily data from each site to estimate the effect that indoor basement humidity and outdoor humidity had on dehumidifier energy use. We found that high indoor basement humidity was linked to low dehumidifier energy use and that high outdoor humidity was linked to high dehumidifier energy use. We found these relationships to be ef-fective predictors of dehumidifier energy use in general. However, the predictive ability of this model was highly variable across sites and proved to be a good fit only for dehumidifiers that were able to maintain reasonable control over basement humidity levels. For those cases where dehumidifiers did not effectively control humidity, we switched our model around and used dehumidifier energy use as a predictor of basement humidity ratios.

Clearly a relationship exists between the amount of energy used for dehumidi-fication and basement humidity levels. Homes that maintained lower daily hu-midity levels in the basement used more energy for dehumidification than homes that maintained higher daily humidity levels in the basement. During summer months, nearly half of the basements we monitored maintained a daily average RH of less than 50%. These homes used an av-erage of 4.2 kWh per day more than the homes where the basement maintained a daily average RH exceeding 50%.

Figure 1 illustrates the general re-lationship between basement RH lev-els and average daily dehumidification energy use. Data for the 40 sites are ar-ranged from left to right in order of in-

creasing average energy use per day. The bars in the top panel (representing the 25th and 75th percentiles of daily average basement RH levels) show the variability in humidity control across all 40 sites. We found that basement humidity levels were relatively well controlled at some of the sites we metered (RH levels fluctuated only 1–2%), while at other sites we me-

the midwest energy survey is a tracking study initiated by the energy center of wisconsin in 2007 to measure public attitudes, awareness, and practices on energy efficiency and cli-mate change. the study is entitled climate change and energy: tracking public opinions and

responses, and it is available from the energy center of wisconsin.In this independent research conducted in nine midwestern states in 2007, and ex-

panded to the united states as a whole in 2008, the energy center links public concern about energy efficiency and climate change with opportunities for improving the design of utility and other energy efficiency programs and with increasing energy savings. Analysis of the results reveals▪ gaps between efficiency opportunities, perceptions, and practices, highlighting the need

for better energy education; ▪ a snapshot of policy approaches to addressing carbon pollution that are most likely to

win public support; ▪ a trend showing how public concerns about climate, the environment, and energy ef-

ficiency fare over time relative to other public concerns; and ▪ how much reliance customers place on their utility company for help with saving energy.

For more information on the midwest energy survey, including a free webcast on results of the most recent survey, visit www.ecw.org/mwenergysurvey. this webcast was produced by the energy center of wisconsin and presented by Ingo Bensch, a senior project manager at the energy center of wisconsin.

25

30

35

40

45

50

55

60

65

70

75

Rel

ativ

e H

umid

ity(%

)

Daily Medians and Interquartiles for Basement Relative Humidity, by Site

0

3

6

9

12

15

kWh

Daily Average Dehumidifier Energy Use (kWh), by Site)

Figure 1. top panel: Box plots of daily average basement rh for 40 wisconsin homes, arranged in order of increasing daily average dehumidification energy use. site-specific median values of daily average rh are indicated by orange diamonds. the 25th and 75th percentiles of daily average rh are indicated by blue bars. bottom panel: Average daily energy use for each site during summer months, shown in order of increasing magnitude.

Daily Medians and Interquartiles for Basement Relative Humidity, by Site

ABoUT THE MiDWEST EnERgy SURvEy

appliances

46 Home Energy | Januar y/Februar y 2011

tered, basement humidity levels were controlled very little, if at all (RH levels fluc-tuated 10–20 %).

DEHUMiDifiER DUTy CyClESDehumidifier duty cycles var-ied greatly across sites. We divided duty cycles into three modes of operation: Off, Fan-Only, and Run. Off mode consists of periods when nei-ther the compressor nor the circulation fan is operating. Fan-Only consists of periods when the circulation fan is operating, but the compressor is not. Run mode consists of periods when both the com-pressor and fan are operating.

Dehumidifiers in our sample drew 40–120 watts, for an average of 75 watts, when in Fan-Only mode. They drew 300–700 watts, for an average of 500 watts when in Run mode. Figure 2 shows the average summer and fall duty cycles for the 40 dehumidi-

fiers in our sample. Note that although the average dehumidifier ran 56% of the time during summer months, we found that indi-vidual duty cycles varied greatly. Some of the units we metered were in Run mode as little as 15% of the time, while other units ran virtually nonstop.

SURvEy RESponSES on DEHUMiDifiER USEThe most recent MES survey showed that almost 65% of Wisconsin homes have a stand-alone dehumidifier. A compar-ison of our survey results and the MES survey indicated that more dehumidifiers were installed in WESH homes (75%) than in non-WESH homes of a similar age (46%). The frequency and

For more information call: 1-877-FAN-CONTROL

www.AirCycler.com (1-877-326-2668)

www.AirCycler.com

It’s simple, it’s smart, it’s easy...

Patent Pending. Cover plate not included. Use any standard switch plate.

The Most Economical Ventilation Solution!

SmartExhaustTM

Light Switch, Bath Fan Switch, Fan Delay Timer & Ventilation Controller ... All in a Single Switch!

u Make standard bath fans ASHRE 62.2 compliant

u Microprocessor technology provides precise ventilation times.

u Manual fan operation is subtracted from set ventilation time.

u Fan runs every hour for set ventilation, less any manual and delay operation.

u Excess manual and/or delay operation is subtracted from next hours ventilation time.

u Great for - Meeting ventilation codes, Reducing Mold, Mildew & Pollutants, Saving energy and you money! switch plate.

1) Do not connect this device to aluminum wire. Use with copper or copper clad wire only.

2) TURN POWER OFF at circuit breaker of fuse panel.

3) Remove cover plate and existing switch from wall box if there is one already installed.

4) Connect the wires in the wall box using the supplied wire nuts. Wires must have ¾ inch of bare copper exposed. Twist wires together tightly with supplied wire nuts. Make sure no bare copper is exposed. Secure connections with electrical tape. If a light is not connected, be sure to attach a wire nut to unused blue wire and secure with electrical tape.

5) Mount SmartExhaust™ switch in to wall box with supplied mounting screws.

6) Set desired DELAY time by turning dial to desired minutes.

7) Set desired VENTILATION time by turning dial to desired minutes per hour.

8) Turn on power at circuit breaker or fuse box.

Operating instructions:

Move toggle switch up to turn on fan and light.

Move toggle switch down to turn off light. Fan will run for set DELAY time.To cancel DELAY time, move toggle up again for at least 1 second then down again.Fan will shut off, cancling set delay time.

Delay will not activate if light/fan has not been on for at least 10 seconds.

Fan will automatically come on once per hour for set VENTILATION time.

Any manual fan operation and DELAY operation will be subtracted from VENTILATION time for that hour. If manual fan operation and DELAY operation exceed set VENTILATION time, the excess time will be subtractedfrom the next hours VENTILATION time.

FOR SUPPLY CONNECTIONS, USE 18 AWG OR LARGERWIRES SUITABLE FOR AT LEAST 105 ˚C

Black - Hot

Green - Ground

White - Neutral

Blue - Light hot

Red - Fan hot

Ventilation

SmartExhaust™ Instruction Manual

Ventilation

411 Plain StreetMarshfield, MA 02050

A Division of Lipidex Corporation SmartExhaust is a registered trademark of Lipidex corp.Patents and Patents pending.

1-877-FAN-CONTrol (326-2668)

Example: 10 minute delay, 20 minutes per hour ventilation

table 1. MeS Responses Regarding Frequency and estimated Levels of Dehumidifier Use

FrEquENCy oF uSE* Wisconsin Homes with Dehumidifiers

Percentage estimated kWh/yr

Seldom 7% 0

Part of summer 32% 265

all summer 33% 530

Summer and other seasons 28% 779

Weight average 477

*Based on 837 responses to the Midwest Energy Survey.

A Division of Applied Proactive Technologies, Inc.

0%

20%

40%

60%

80%

100%

Average Dehumidifier Duty Cycle

Summer Fall

RunOff Fan Only

average Dehumidifier Duty Cycle

Figure 2. Average duty cycles of dehumid-ifiers in 40 wisconsin homes during the summer and fall months of 2009.

appliances

48 Home Energy | Januar y/Februar y 2011

duration of reported dehumidifier use was consistent across surveys; about 60% of respondents reported using their dehu-midifiers during the entire summer or more.

In the latest MES, we found that nearly half of the dehumidi-fiers used in newer homes in Wisconsin were connected directly to a drain (rather than draining into a manually emptied drain pan). Dehumidifiers using drain pans are susceptible to periods of inoperation when occupants fail to empty the pans regularly. We found that the percentage of dehumidifiers connected directly to a drain was significantly higher in WESH homes (80%) than in non-WESH homes (45%). Homes in our metered sample where the dehumidifier was connected directly to a drain used slightly more energy than those where the dehumidifier was drained manually; however, the difference was not statistically significant.

A principal goal of our field study was to estimate average an-nualized energy use for de-humidifiers in Wisconsin. We used survey responses and the metered usage data from the 20 randomly se-lected homes to estimate that, on average, dehumidi-fiers in Wisconsin consume 477 kWh per year. This estimate is subject to the

variation in use that we observed across the sites in our field study. The values used to arrive at this estimate are shown in Table 1. In generating this estimate, we assume that the average Wisconsin household uses its dehumidifier during a 90-day summer and a 60-day nonsummer period, in a manner that is consistent with use in the 20 randomly selected homes that we monitored.

MAxiMiZE DEHUMiDifiCATion, MiniMiZE EnERgy USEIn summary, our study suggests that households in Wisconsin use a significant amount of energy to dehumidify their homes. In addition, the degree to which dehumidifiers are used over the course of a year can vary dramatically, with some units remaining idle most of the year and other units running vir-tually nonstop. Households in the upper quartile of use could easily consume more than 1,000 kWh per year to dehumidify their homes. We found that all homes in the upper quartile maintained daily basement RH levels of less than 50%, and several of these homes maintained RH levels of less than 40%. Helping households to determine the dehumidifier settings that minimize energy use but maintain adequate levels of de-humidification may give Focus on Energy an opportunity to promote home energy conservation.

Andy Mendyk is a project manager and Dan Cautley is a senior project manager at the Energy Center of Wisconsin.

>> For more information:

the complete study described in this article, Dehumidification and Subslab Ventilation in Wisconsin Homes, is available through the energy Center of Wisconsin at www.ecw.org/dehumidifier. to learn more about the energy Center of Wisconsin, go to www.ecw.org.

Applied EnergyProducts & Sales

Complete Home Weatherization Materials800-255-7996

www.appliedenergyproducts.com

appliances