How to Diognose Refrigerant Overcharge, TXV System

When a system with a TXV metering device is overcharged, the suction pressure and superheat may appear normal.  The normal conditionsare a result of the TXV regulating the refrigerant flow independent of the compressor.

The excess refrigerant is stored in the condenser coil and increases the head pressure and liquid subcooling.  If the charge is high enough the suction pressure may be elevated with a slightly low superheat.

Higher pressures increase power required for system operation.

Remove refrigerant in accordance with the manufacturers instructions to obtain the desired or target subcooling.

Testing a Property’s Building Envelope For Infiltration

Specialized building inspectors utilize a device called a “Blower Door” to assess and aid in the buildings air tightness.

Benefits resulting from an air tight structure include:

  • Reducing energy usage attributed to air leakage.
  • Avoiding humidity or moisture build-up causing water condensation problems.
  • Avoiding unpleasant drafts created by cool air leaking in by way of the outdoor environment.
  • Making certain that the properties air quality is properly ventilated.

How They Work

A “Blower Door” is a strong fan that mounts directly into your exterior doors framework.  The fan draws air out of the building, decreasing the air pressure inside. The greater outdoor air pressure enters the building by means of unsealed crevices and voids in walls, windows and ceilings. The inspectors use a smoke pencil to help discover air flow leaks.  Such assessments verify the air infiltration rate for a building.

“Blower Doors” are constructed of a framework and adaptable section which fit within a doorway.  A variable-speed fan and pressure gauge determine the pressure differences indoors as well as exterior to the property, and an airflow manometer and tubes are used to gauge airflow.

There are two kinds of blower doors: calibrated and uncalibrated. It is essential that auditors make use of calibrated Blower Door Units. This particular type of blower door features numerous gauges which assess the quantity of air drawn out of the building through the fan. Uncalibrated blower doors will simply identify leaks in properties. The uncalibrated units offer no method for analyzing the over-all air tightness of the building. The calibrated blower door’s information permits the inspector to assess the quantity of air leakage as well as the success of any air-sealing work.

Planning for a Blower Door Test

Complete the following measures to get your property ready for a blower door test:

  • Close windows and open up inside doors.
  • Turn down your thermostats for heating units as well as water heating units.
  • Cover ashes in wood stoves and fire places with moist newspapers.
  • Shut fireplace dampers, fireplace doors, and wood stove air intakes.

A Blower Door test and the resulting sealing of the building envelope will return energy savings for years to come.

How Much Does Your Heat and Cool Unit, Heat and Cool?

If You Purchased a 3 Ton, 14 SEER Heat Cool Unit, What Size Unit Did You Really Get? 

Your system can be tested to find out.

Under extreme conditions your new 3 ton unit may only have a 1.5 ton and 7 SEER efficiency.  Under normal conditions your unit might only measure up to only 90% of its nameplate rating. If your unit is over 12 years old it may have lost significant capacity and efficiency.

About 70% of your heat and cool air conditioner units capacity is used to lower the temperature of the air.  The remaining 30% capacity is used to remove humidity or moisture from the air.  As an example a 3 ton unit should have a total capacity of 12000 btu’s per ton or 36000 btu’s.  Of the 36000 btu’s, 24000 btu’s would lower the temperature of the air and 12000 btu’s would remove moisture from the air.  In order to measure total capacity, we will need to measure both. 

A normal thermometer will measure the air temperature entering the return of your AC and the temperature of the colder air can be measured at the first supply vent.  If you multiply the difference in temperature by 1.08 btu for each cubic foot of air flow produced by the Heat Cool system, you have the capacity measure that lowers the temperature.  This measure is called sensible heat.

Another thermometer called a psychrometer or hygrometer is needed to measure the humidity that is removed by the air conditioner.  A psychrometer is a normal thermometer with a wet cotton sock over the bulb.  The temperature reading called wet bulb temperature can be converted to a value indicating the temperature and grains of moisture in the air.   This value is called latent heat and enthalpy.  You can purchase or make a wet bulb thermometer.  A very accurate digital hygrometer that measures % relative humidity can be purchased for around $100.  Using an enthalpy chart or enthalpy calculator available online, you can convert your measurements to btu’s.  It is very important to measure wet bulb temperature within one tenth of a degree F.

The more difficult measure to obtain is the amount of air flow in cubic feet per minute (CFM).  An instrument called a vane anemometer can be used as can an instrument to measure static pressure.  Instruction videos for measuring air flow in CFM can be found on

The Formula

Calculating total Btu’s involves measuring airflow and wet bulb air temperatures in and into a conditioned space. Total Btu’s are calculated using the formula:

Total Btu = 4.5 X CFM X Enthalpy Change

The 4.5 factor represents the weight of 1 cubic foot/minute (CFM) of standard air per hour.

CFM is the total supply airflow entering the building from the system.

Enthalpy change is measured using a hygrometer and converting the readings to Enthalpy.

Latent eat = Total Heat – Sensible Heat


  • Air and heat can leak into the system between your temperature readings and the indoor cooling coil.  If this happens, your calculation will indicate the cooling delivered to the space and not the cooling produced by the AC unit.
  • You can also determine equipment airflow by carefully measuring fan static pressure, then plotting the fan CFM based on the manufacturer’s fan data
  • An enthalpy change of about 6 is normal.
  • Airflow has a major effect on system performance. It must be measured accurately with top quality instruments and procedures.
  • A humidity level of 90% plus from the supply side of the system is common. As the air is cooled is can hold less moisture.
  • Normal sensible/latent ratio is 70/30.  A significant return air duct leak from a hot attic, produce a 55/45 sensible/latent BTU ratio.

IAQ Indoor Air Quality Alternate Method Saves Up-Front Cost, Plasma Air Ionization

The primary method for reducing indoor air pollution is to dilute the polluted indoor air with outside air.  Building codes assume that the outside air is cleaner than the inside air.  Outside air is not always cleaner than the inside air.

Many of the indoor pollutants emmited into the air originate from people.  Generaly ac/heat systems are designed to introduce 20 cubic feet of outside air into the building per minute per person.  This is raw air and must be cooled, heated, dehumidified or humidified.  Substantial energy is used to treat this outside air.

99.8% of all airborn particles pass through a typical filter.  Agglomerating smaller particles into larger ones using  plasma air ionization improves filter efficiencies.  The smaller particles stick together and fall to the floor or are removed by the filter.

An alternate method seldom used is to remove pollutants from inside air vs the common method of diluting the inside air.  ASHRAE (Association of Heating Refrigeration Air Conditioning Engineers) and IMC (International Mechanical Code)both allow for the reduction in outside air introduced into by using the IAQ procedure.

Another benefit of using the IAQ method is the reduction of the size equipment required to maintain the space temperature.  This reduces the up- front cost of installing a new system and the operating cost of the system.

Calibrate Thermostats

Periodically walk through the building and compare the thermostat setting with a hand-held digital thermometer (preferably one measuring to 2 decimal places – not the IR version which is inaccurate).  Ensure thermostat setting equals actual space temperature by using a NIST calibrated sensor. This will also reduce the number of dueling zones and decrease the occurrence of simultaneous heating and cooling.

US Energy Efficiency Incentives


The DSIRE web site provides information about renewable energy and energy efficiency incentives and policies in effect in the United States. Relevant incentives and policies established by the federal government, state governments, local governments, electric utilities and non-profit organizations are included in DSIRE. Continue reading “US Energy Efficiency Incentives” »