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Corn Comfort - Temperature Relative Humidity

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  • Harry & Linda Clift
    What is the healthy room temperature and relative humidity? Relative Humidity (RH) – 50% is the healthy room RH. 50% RH does not exist at any known place on
    Message 1 of 1 , Feb 2, 2005
      What is the healthy room temperature and relative humidity?
      Relative Humidity (RH) – 50% is the healthy room RH.
      50% RH does not exist at any known place on the surface of the
      earth where natural temperature swings eliminate the possibility.
      Allergies, colds, flue, germs, molds, mildews, viruses sustained at
      50% RH went the way of the dinosaur to become extinct where humans

      Why not keep the room at 50% RH?
      Conventional HVAC systems can not control RH within 10% accuracy.
      Linda can control the RH better with a pan of water on the range
      than an expensive HVAC system. Why?

      High RH – At 70%-100% RH germs, molds, mildew, and viruses thrive
      and multiply fast at room temperature.
      Black mold thrives inside a dark wall that has 100% RH sustained by
      a roof leak. HVAC duct drains become clogged with
      living, thriving, growing green goo.

      Low RH – At 0%-30% RH the "desert" germs thrive and multiply.
      Moisture loving molds and mildew may dry and die but
      static electricity energizing dust, pollen, allergies, flue,
      sinuses, viruses, colds, dry skin, and chapped lips.

      Why does RH swing?
      RH swings with temperature.

      What temperature is healthy and feels good at 50% RH?
      "A stable temperature is required to maintain a healthy RH".

      I set the thermostat and didn't change it. Why does temperature
      The typical HVAC system will swing room temperature 5 to 15 degrees
      F. Check the span between the high and low "on to off" heat shut
      down and the "off to on" heat turn on. For the total temperature
      error add the thermostat error of 2-7 deg F to the controllable span
      of 5-15 degrees F.

      A stable temperature maintains a constant RH.
      A room at 60 deg F and 100% RH may feel 70 deg F.
      Increase the temperature to 70 deg F and the RH will automatically
      be lowered and more healthy.

      A corn stove maintains a constant room temperature. The Relative
      Humidity is stable.
      Now you know why corn stove owners love the "feel" of corn stove

      Water Pressure is the force that drives RH. The partial pressure of
      water vapor is maximum at 100% RH.
      Total pressure, atmospheric or barometric pressure averages 14.696
      psia at sea level or less at high elevations.
      Total pressure is the sum of all the partial pressures of each
      The partial pressure of water vapor in the air is constantly
      changing as the RH changes.
      The RH is constantly changing because of the HVAC temperature
      Available oxygen supply to the skin and lungs is inversely
      proportional to the RH induced water vapor pressure in the air.
      Add a few allergies, germs, viruses, dry skin conditions and colds
      that multiply rapidly at room temperature
      – how do we ever survive?
      Relative Humidity Measurement
      Relative humidity (RH) is defined as the ratio of the water vapor
      pressure or water vapor content to the saturation vapor pressure or
      the maximum vapor content at the temperature of the air or gas. The
      saturation vapor pressure in the air varies with air temperature,
      the higher the temperature, the more water vapor it can hold. When
      saturated the relative humidity in the air is 100 %RH.
      Dewpoint Measurement
      Dewpoint is the temperature at which air becomes saturated with
      water and begins to condense - forming dew. Therefore at 100 %
      relative humidity the ambient or process temperature equals the
      dewpoint temperature. The more negative the dewpoint temperature is
      from the ambient temperature, the smaller is the risk of
      condensation and the drier the gas or air stream.
      Barometric Pressure Measurement
      Barometric pressure is defined as atmospheric pressure i.e. the
      force exerted on a surface of unit area caused by the weight of the
      air column above, normally between 950 - 1050 hPa at sea level. It
      indicates the presence and movement of weather patterns and affects
      many physical measurements.
      Why Measure Relative Humidity?
      Humidity has a significant effect on our environment. Humidity
      measurement gives us an opportunity to control these effects.
      The significance of indoor air quality to our health has become
      evident. Humans are best suited to and feel most comfortable at
      certain humidity and temperature; excess high or low humidity or
      temperature cause discomfort.
      As most materials are hygroscopic, their water content always tries
      to reach equilibrium with the surrounding relative humidity. Thus
      each material has its own ideal storage humidity which should be
      maintained. Too dry or too humid conditions can destroy the material.
      In many production processes the correct measurement and adjustment
      of humidity is extremely important for sustaining the high quality
      of products and the correct level of energy consumption. The right
      humidity makes it possible to optimize energy consumption and
      improve end product quality as well as product yield.
      At low humidity, static electricity increases. This can be crucial
      in the chemical industry where dry powdery material is handled. In
      extreme cases static electricity can cause explosions.
      Moisture measurement in construction materials. Excess moisture in
      structures can cause quality and health problems and economical
      losses. Concrete is usually dryer on the surface than deeper down in
      the structure. Therefore, a structural humidity profile including
      measurement data at different depths is the most reliable approach.
      Vaisala's product variety includes humidity transmitters especially
      designed for the measurement of structural humidity.

      Carbon Dioxide Measurement
      Carbon dioxide (CO2) is one of the most common gases in our
      atmosphere. It is formed during breathing of humans and animals, in
      fermentation and decomposition processes and during the burning of
      fossil fuels. Plants need carbon dioxide in the assimilation
      process. It can therefore be used as a fertilizer to enhance plant
      growth. Carbon dioxide is a good indicator for indoor air quality.
      In large concentrations carbon dioxide is a potential safety hazard
      and it inhibits bacterial growth.

      Diverse CO2 applications
      There is a growing need for reliable measurement of carbon dioxide
      in environments as diverse as bottling plants and greenhouses, and
      classrooms.The lack of small, reliable and inexpensive instruments
      has made CO2 measurement difficult and costly. Furthermore, carbon
      dioxide is used in many industrial processes, from refining sugar to
      hardening molds in foundries. Carbon dioxide is often used to
      displace oxygen e.g. in process and packing industries. Fires and
      explosions can be prevented by carbon dioxide enveloping.
      Potential safety hazards
      When the concentration of carbon dioxide rises, people start to feel
      tired and listless and have trouble concentrating.With further
      increases, CO2 begins to act as an asphyxiant.Carbon dioxide which
      is an odorless, colorless gas, displaces air and oxygen in it. CO2
      is denser than air, and high concentrations can occur in open pits
      and other areas below ground level. Exposure to very high
      concentrations of carbondioxide results in unconsciousness or even
      death. Occupations where carbon dioxide can rise to dangerous levels
      include the brewing and carbonated drink industries,the freezing of
      food with dryice, cold storage, cargo ships,and of course plants
      where CO2 or dry ice is produced or handled.
      Beneficial effects in greenhouses
      On the positive side, carbondioxide can enhance plantgrowth. In
      greenhouses, the growth rate and development of plants, ranging from
      tomatoes to roses, can be improved by controlling the concentration
      of carbon dioxide. This raises the productivity and quality of the
      crops. To reduce the carbon dioxide consumption and to maximize the
      productivity, the CO2 level is typically monitored and measured. If
      the carbon dioxide level rises too high, the plants can be damaged
      and their growth stunted
      Source: http://www.vaisala.com/thumbnail.asp?Section=5613

      Corn Stoves and Air Quality Control
      Recirculation of filtered room air through the extreme internal heat
      of the corn stove kills germs, mold and mildew improving the quality
      of the air. The technical reason to keep the corn stove running
      while gone to work is shown below. The technical article on Air
      Quality Control demonstrates the importance of the corn stove
      maintaining 40-60% relative humidity. The partial pressure of water
      vapor equalizes from the outside to the inside. Corn stoves
      effectively drop the % RH by maintaining an increased inside
      temperature at all times preventing the outside water vapor pressure
      from forcing excess water vapor into the insulation of the walls and
      Without the affordable warmth of a corn stove in the winter months,
      insulation in the walls and ceiling of a home become saturated with
      moisture inside the home. In contrast, moisture from outside the
      home infiltrates the insulation of a home during the summer months
      and will condense inside the walls and between double panes windows
      unless it is removed prior to the cool winter weather. The vapor
      barrier is installed on the interior side of the wall to prevent
      inside moisture from condensing inside the walls during winter
      months. The vapor barrier is actually counterproductive in the
      summer months trapping outside moisture inside the walls. Moisture
      condenses in contact with a cold surface such as a glass window pane
      or the cold surface inside the wall. Moisture trapped inside the
      walls during summer months, if allowed to remain, will condense
      during cold weather and result in molds, mildews, and eventually
      structural damage. The warmth from the corn stove takes
      approximately two weeks to penetrate the walls and reduce the 70% RH
      to 50% RH inside the insulation of the walls and ceiling. A casual
      observation notes a distinct lighter wall color at 50% RH as
      compared to 70% RH.
      Keep the corn stove running to keep the walls warm and dry. Dry
      walls are insulators from the outside cold and reduce the energy
      bill. Wet walls are conductors, promote heat transfer to the
      outside, and increase the energy bill. The "R" value of the wall,
      ceiling, and floor was conducted under ideal conditions with no
      consideration for moisture infiltration. For these reasons, the
      corn stove is even more important for super insulated homes than for
      the average air infiltrated home. The insulation must be kept dry
      in order to be effective.
      Caution the article is technical and not well written but the sketch
      is accurate.
      Air Quality Control
      In 2003, hundreds of North Carolina Central University students were
      forced to evacuate campus housing as the school spent millions of
      dollars to eradicate toxic mold from new dormitories. Meanwhile,
      Duke University had to shut down its engineering library to tackle
      mold growth in its book collections. Where was the mold coming from?
      And why?
      In a word, pressure. The key to mold and fungal growth is moisture,
      and in both cases improper building pressurization resulted in high
      internal humidity levels greater than 70% relative humidity that
      encouraged mold production and replication within the buildings.
      Building pressure has a significant role in water transport across
      the building envelope. Control of a building's pressurization flow
      is essential for the reduction of mold and fungal growth (see figure
      1), but how can it be done cheaply and efficiently?

      Airflow/temperature measuring devices are used to maintain dilution
      (outside air) flow rates and building pressure essential to
      acceptable indoor air quality (IAQ). They are also routinely used in
      laboratory and healthcare institutions for contaminant and infection
      IAQ can be substantially improved through the proper control of
      outdoor air intake flow. Dilution airflow control is essential to
      maintaining acceptable contaminant levels. Indoor pollutants are
      generated from components within the building as well as its
      occupants. Minimum outdoor air ventilation levels must be maintained
      to provide adequate dilution. Therefore, direct measurement of
      outdoor airflow rates is essential for acceptable IAQ. Verification
      is a requirement of both ASHRAE Standard 62, Ventilation for
      Acceptable Indoor Air Quality and the International Mechanical Code.
      Proper control requires accurate and reliable airflow measurement.
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