This discussion consists of my personal subjective, undocumented and unverified opinions concerning residential mold and mildew. I welcome any and all comments from any and all interested parties that are interested in this matter.
Many residential homeowners located in the high ambient humidity locations close to the Gulf of Mexico and the East Coast are experiencing high relative humidity plus mold and mildew forming in the occupied areas of their houses. I would like to facilitate an open discussion of this situation with the hope of documenting the causes, extent, and possible remedies to correct this problem.
I am Gerald R. Spencer, P.E. and I am the Mechanical and Electrical Engineer of Record for the design and the construction of many new military family housing units, the remodeling of the HVAC for many existing military family housing units, and for energy conservation (ECIP) modifications to many existing military family housing units.
Many new residential homeowners located in the high ambient humidity locations close to the Gulf of Mexico and/or the East Coast are experiencing high relative humidity, mold and mildew forming in the occupied areas of their houses. I would like to facilitate an open discussion of this situation with the hope of documenting the causes, extent, and possible remedies to correct this problem.
I also have residential HVAC design experience for many privately owned high end residential construction projects over the past 50+ years. Many new residences in high ambient humidity areas are complaining about the Formation of Mold & Mildew.
These occurrences were not as prevalent until recently in the last 20+ years.
The current energy consumption efficiency government requirements expressed as SEER ratings are marketed with higher SEER numbers reflected as more (sensible) cooling into and less moisture removal from a house for the same amount of electricity purchased.
The residential HVAC manufacturers do not mention that the lower electrical cost benefits are achieved by providing less latent cooling, and this is the main cause of Mold & Mildew creation in newly constructed residences.
Sensible cooling is the refrigerated cooling effect measured by regular thermometers similar to the thermometer that you measured your body temperature before electronic thermometers were invented.
Latent moisture cooling effect is the cooling that occurs when moisture is removed by condensation at the cooling coils by the refrigerated cooling effect when the cooling coil surface is lower than the dew point of the air being cooled at the cooling coil.
The dew point of the indoor or the outdoor air is the temperature where moisture (dew) will begin to condense onto a surface of that temperature in that air.
The total amount of moisture in the indoor or in the outdoor air is proportional to the dew point temperature. This increase in efficiency is obtained by increasing the heat transfer area of the indoor coil and the outdoor coil, plus also increasing the air circulation through the indoor coil.
These modifications allow and cause the refrigerant suction temperature (balance point) to increase and produce more sensible cooling and less latent moisture cooling.
Because less work is required to do the same amount of sensible cooling but less coincidental moisture removal (latent) cooling than before these equipment operating temperature changes, this results in less moisture removal in the residence and produces higher SEER equipment ratings.
More moisture in a residence is one of the major factors in the creation of Mold & Mildew within any new or any old residence. Relative humidity is the percent of moisture measured compared to the 100% saturation of that indoor or outdoor air.
This is useful because indoor moisture can exceed the points where mold and mildew are created for short time frames without creating mold and mildew if these times are followed by periods of low humidity created by the air condition system to cause evaporation of moisture condensed and absorbed by the materials that were used for construction and also the contents of the occupied spaces.
This is like a flywheel effect where moisture content varies hourly due to moisture creation and influent (from cooking, washing, infiltration, dish drying, bathing, etc,) in the occupied spaces and the moisture removal by the air conditioning system.
Residences located within a geographical area that has more continuous hours with high ambient humidity in the atmosphere will generally need more latent moisture cooling capacity to keep the moisture within the occupied space of the residence low enough to prevent the formation of mold and mildew in the occupied spaces.
This time/moisture relationship is analogous to the cooking time/cooking temperature relationship and hard to scientifically quantify. This requirement varies with the tightness that the residence is sealed and gasketed to minimize moist air infiltration entering the occupied space which will require additional latent moisture cooling to keep the moisture content below the limits where mold and mildew are created or formed.
This requirement varies with the residents activities creates moisture occupied space which will require additional latent moisture cooling to keep the moisture content below the limits where mold and mildew are created or formed.
These requirements vary from household to household with more variables affecting the amount of latent moisture cooling that will be needed to keep the moisture content below the limits where mold and mildew are created or formed in each different household.
1. Lower the system Apparatus Dew Point (ADP) by installing a thermostatic expansion valve that will open refrigerant liquid flow as required to maintain a lower 38-40 deg F suction temperature on the Refrigerant line leaving the evaporator coil and decrease the air flow at the evaporator coil to increase the latent cooling. This will decrease the sensible cooling and require more refrigeration capacity to maintain room temperatures.
2. More additional cooling capacity will be required for the existing system after these modifications to maintain room temperature are completed. install another additional system to maybe serve only the bedrooms. Maybe disconnect the branch ducts to the bedrooms from the main system and then connect those branch ducts to the additional new HVAC system. Maybe consider running only one of the HVAC systems during the day to cool the entire house, so that system will operate more hours each day, and therefore do more de-humidification by lessening the number of compressor run cycles each day when the moisture on the indoor coil evaporates back into the occupied spaces each time that the compressor cycles...
Gerald Spencer, P.E. has more than 50 years experience serving as the Engineer of Record responsible for the design and construction of the MEP portions of more than 1300 building construction projects since 1968 including more than 30 years of preparing forensic engineering reports. Gerald Spencer, P.E. has also been providing licensed professional engineering expert opinion and testimony concerning HVAC, electrical, plumbing, cryogenics, ventilation, construction contract compliance, construction cost estimating, construction contract acquisition, construction contract administration, and other construction matters for attorneys with since 2001.
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