Tulsa commercial contractors must have knowledge of mechanical, electrical, and plumbing trades, even though they are not licensed, to be able to properly oversee their installation. Most jurisdiction will have a representative inspect these trades at varying levels of completion. For Mechanical or HVAC knowledge a Tulsa commercial contractor must have knowledge of psychrometrics. There are seven properties of air that are considered. The American Institute of Constructors, or AIC, explains the seven properties of air as follows:
“… Dry bulb temperature (DB) is the air temperature and is the measure of sensible heat.
- Wet bulb temperature (WB) is the air temperature measured with a thermometer with a wet cloth sock over it. As the water in the sock evaporates, the temperature on the thermometer is lowered through the latent heat of the evaporation process. Wet bulb and dry bulb temperatures are equal only when the air is 100% saturated (100% RH) and no evaporation can take place. When the air is not 100% saturated, the wet bulb temperature will always be lower than the dry bulb temperature. The wet bulb temperature is the lowest temperature that air can be cooled by the evaporation of water.
- Dew point temperature (DP) is the temperature at which the water vapor in the air begins to condense. At this point, the air is 100%saturated and cannot hold any more water vapor. Relative humidity (RH) is the ratio of moisture in the air compared to how much that same sample of air could hold and is expressed as a percentage. Air that is holding .008 lb of water but has the capacity of holding 0.10 lb would have a relative humidity of 80%.
- Humidity ratio or absolute humidity (W) is the amount of water in 1 lb of dry air. It is expressed as either grains of moisture per pound of dry air (gr/lb) or pounds of water per pound of dry air (lb/lb). A grain of moisture is 1/7,000 lb. This is a measure of latent heat in the air.
* Specific volume (v) is the physical size or volume of 1 lb of dry air. As air is warmed and humidified it gets larger. As it cools and dehumidifies, the same mass of air gets smaller.
* Enthalpy (h) is the total amount of thermal energy (sensible and latent) in the air. It is measured in BTUs per pound of dry air…”
The Tulsa commercial contractor must be able to read a psychrometric chart. The AIC describe the psychrometric chart in this way:
“…the psychrometric chart is a graphical representation of the seven properties of air described above. If you have two properties of air you can locate a point on the chart and determine the remaining five air properties… or an example of a psychrometric chart. All of the information provided on the chart is for 1 lb of air. In the HVAC industry it is usually the difference between two points that is of interest. For example, a technician may want to know the different air properties of inside and outside air. Points that move toward the right on the chart represent air that is being heated. Points that move up the chart represent air that is being humidified. Points that are moving to the right and up are being heated and humidified…”
Tulsa commercial contractor’s also need to understand electricity. The first distinction is between AC and DC power. The AIC describes AC and DC power and the difference between power and energy in the following manner:
“…Direct current is the flow of electrons in a single direction. Batteries provide direct current because the electrons flow in a single direction from the negative to positive terminal. With alternating current the electrons alternate the direction of the current. In the United States the frequency (f) is 60 hertz (Hz), which means that the direction of the current changes 60 times a second. Building power is alternating current… In single-phase AC circuits, power is the product of Volts × Amperes, which is referred to as apparent power and is the power available to use… he unit of measure for AC power is the watt (W) or kilowatt (1,000 W; kW). When the peak voltage and amperage align, the power is said to be in phase. In this case, Watts = Volts × Amps. However, many appliances, such as motors and computers, cause the peak voltage and amperage to be out of phase with each other. When they are out of phase, all of the power available (apparent power) is not used. The actual power used is called real power or working power. The power factor (PF) is a number from 0 to 1 and is a measure of how much of the available power is being used. When the voltage and amperage are in phase, all of the apparent power is used, and the power factor is 1. When only some of the apparent power is used, the power factor will be less than 1…
… Power and energy are not the same. Power is the rate of energy transfer. In a building, power is how much electricity is being used at any given point in time. A 60 W lightbulb is consuming 60 watts per second. It’s a rate of energy consumption. Energy is the ability to do work and is quantifiable. It’s the rate of consumption multiplied by time…”
The way electricity is controlled and measured in way to make it useful is through Ohm’s law. The AIC describes Ohm’s Law as follows:
“… Electrical energy is the flow of electrons through a conductor. Following are the basic units that describe electrical circuits:
- Voltage: the electromotive force (EMF) or potential difference that causes an electric current to flow. The unit of measure is the volt (E).
- Current: the flow of electrons, specifically the flow of 1 coulomb (6.24 × 1018 𝑒lectrons) per second passing through a conductor. The unit of measure is the ampere (A).
* Resistance: the internal property of matter that resists the flow of current. The unit of measure is the ohm (R). Materials with low resistance are called conductors. Materials with high resistance are called insulators.
The relationship between voltage, current, and resistance is defined by Ohm’s law:
Voltage = Current × Resistance (E = IR)…”
Tulsa commercial contractors must have knowledge of trades they oversee to be able to ensure proper installation of these systems.