March 20, 2006
Hot-Humid

Abstract: 

This report summarizes indoor temperature and humidity data that have been collected from houses by the Building Science Consortium of the US Department of Energy Building America Program. Data were collected at 43 houses from May 2000 through February 2005. The houses are located in various southern cities, including Houston, Austin, Dallas, Jacksonville, Fort Meyers, Orlando, and Oklahoma City. Most sites were located in the hot, humid gulf coast region. The data collected from the test homes were analyzed to understand when and for how long high humidity occurred in these homes. The analysis also evaluated how closely high humidity and the need for dehumidification corresponded to cooling operation.

1. Introduction

This report summarizes indoor temperature and humidity data that have been collected from houses by the Building Science Consortium of the US Department of Energy Building America Program. Data were collected at 43 houses from May 2000 through February 2005. The houses are located in various southern cities, including Houston, Austin, Dallas, Jacksonville, Fort Meyers, Orlando, and Oklahoma City. Most sites were located in the hot, humid gulf coast region.

The data set includes "high performance" houses that were designed and built to Building America standards as well as standard houses that were monitored in order to establish a baseline. Many of the houses included enhanced air conditioners (e.g., means to improve moisture removal), or dehumidifiers, or energy recovery ventilators (ERVs). Most houses also included an explicit means to deliver ventilation air to the conditioned space.

Battery-powered HOBO dataloggers to measure temperature and humidity were placed in various locations in the conditioned space and in some attics. Campbell dataloggers were also installed at some test sites to measure the runtime/status of the cooling, heating, dehumidification and ventilation systems. Data were collected at hourly intervals for several months at each site. The data collected from the test homes were analyzed to understand when and for how long high humidity occurred in these homes. The analysis also evaluated how closely high humidity and the need for dehumidification corresponded to cooling operation.

The remainder of this document is organized into the following sections:

  • Section 2 describes the test houses;
  • Section 3 lists the instrumentation and data collection techniques as well as the types of data collected from each site;
  • Section 4 describes the data analysis;
  • Appendix A provides Tables showing high humidity events at each site;
  • Appendix B gives Tables showing equipment runtime fractions at each site; and
  • Appendix C presents a set of plots and graphs for each site.

2. House Characteristics

Table 1 and Table 2 summarize the characteristics of the tested homes by builder and location. The homes shaded as gray in the tables are standard home designs while the non-shaded table entries are higher performance Building America or Energy Star designs. The high performance Building America homes were built to an air tightness standard of 0.25 cfm50 per square foot of envelope area. The standard houses typically have at least 50% more leakage.

Table 1: Description of Homes-Builder 1

Table 2: Description of Homes-Builder 2, 3 and 4

In some cases, the homes used cooling systems with enhanced dehumidification features. One
of these homes had a two-stage compressor system, four of them had either: 1) reduced blower
speed when humidity levels were high and overcooling by up to three degrees below the
thermostat setpoint; or 2) always reduced blower speed for the first 5 minutes of the cooling
cycle. Most of the homes had whole-house ventilation systems. Most were of the central-fanintegrated
supply ventilation system type, others had separate ventilation supply fans. Several
types of dehumidification were used at the homes. Including:

  • Stand-alone, Closet. A conventional stand-alone dehumidifier located in a closet, with a louvered door, near the central return air grille.
  • Stand-alone, Return, Attic. A conventional stand-alone dehumidifier located in the attic (which is a conditioned space at these sites). A small branch of the return duct pulls air dehumidified air from the attic to dry the entire house.
  • Thermastor UltraAire. A more efficient dehumidifier that also brought in fresh air from outdoors with a ratio of 1 part outside air to 2 parts inside air. This mixing ratio was required to avoid introducing high dewpoint air directly into cool central supply ducts.
  • Stand-alone, Ducted, Filter-Vent. A conventional stand-alone dehumidifier located in a metal box in the attic. A Filter-Vent ventilation/filtration system pulls air from outdoors (1/3) and the space (2/3) moving that mixed air through the dehumidifier box and then to the central supply ducts.
  • Venmar ERV. A Venmar energy recovery ventilator exchanges heat moisture between exhaust and ventilation air streams.
  • Aprilaire Model 1700. A factory-built, ducted dehumidifier that includes an internal blower able to overcome the static pressure of a central duct system. The unit was installed in the attic.

3. Data Collection

Temperature and humidity conditions were measured at all the sites in one or more zones in the conditioned space. Typically, battery-powered HOBO dataloggers were used. Other dataloggers were installed to measure the runtime of heating, cooling and dehumidification equipment. Table 3 lists the sensors that were installed at each site. Typically temperature and relative humidity (T/RH) were recorded at 2 to 4 locations in the conditioned space in each house. Some sites recorded ambient conditions as well as conditions in the attic.

Table 3: Summary of sensors installed at the test homes

4. Analysis

Tables in Appendix A were designed to break down the measured relative humidity and temperature data into groupings that would facilitate an understanding of when, how often, and how long, relative humidity (RH) conditions existed at each site for every 5% increase between 50% and 70% RH. Temperature data from the thermostat location were included to give an understanding of how the temperature may have affected the indoor relative humidity.

For each house, tables are provided using hourly data based on the following scenarios:

  • The HIGHEST humidity recorded in the space by any sensor,
  • The AVERAGE of all the humidity sensors in the space

Multiple sets of tables are given for a particular site when there was more than 12 months of data available. The year(s) is noted on the top of each page/table. If 12 months or less data are available, the months are all recorded on a single page, even if the data crosses between two years (e.g., “2001, 2002”). In that case, if needed, the year corresponding to each month can be determined from the plots for each site given in Appendix B. . .

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