Many types of meters and gages are available to test al- most any quantity or condition. For example:
- Air–filter efficiency gages
- Air-measurement gages
- Humidity-measuring devices
- Moisture analyzers
- British thermal unit (Btu) meters
Vibration and sound meters and recorders are also available.
Air–Filter Efficiency Gages
Air measurements are taken in an air-distribution system. They often reveal the existence and location of un- intentionally closed or open dampers and obstructions. Leaks in the ductwork and sharp bends are located this way.
Air measurements frequently show the existence of a blocked filter. Dirty and blocked filters can upset the balance of either a heating or cooling system. This is important whether it is in the home or in a large building.
Certain indicators and gages can be mounted in air plenums. They can be used to show that the filter has reached a point where it is restricting the airflow. An air plenum is a large space above the furnace heating or cooling unit.
Air-Measurement Instruments
The volume and velocity of air are important measurements in the temperature control industries. Proper amounts of air are indispensable to the best functioning of refrigeration cycles, regardless of the size of the system. Air-conditioning units and systems also rely upon volume and velocity for proper distribution of conditioned air.
Only a small number of contractors are equipped to measure volume and velocity correctly. The companies that are doing the job properly are in great demand. Professional handling of air volume and velocity ensures the efficient use of equipment. Large buildings are very much in need of the skills of air- balancing teams.
Some people attempt to obtain proper airflow by measuring air temperature. They adjust dampers and blowers speeds. However, they usually fail in their at- tempts to balance the airflow properly.
There are instruments available to measure air velocity and volume. Such instruments can accurately measure the low pressures and differentials involved in air distribution.
Draft gages do measure pressure. However, their specific application to air control makes it more appropriate to discuss them here, rather than under pressure gages. They measure pressure in inches of water. They come in several styles. The most familiar is the slanted type. It may be used either in the field or in the shop.
Meter type draft gages are better for fieldwork. They can be carried easily. They can sample air at various locations, with the meter box in one location.
Besides air pressure, it is frequently necessary to measure air volume, which is measured in cubic feet per minute or cfm. Air velocity is measured in feet per minute or fpm. The measure of airflow is still some- what difficult. However, newer instruments are making accurate measurements possible.
Humidity-Measurement Instruments
Many hygroscopic (moisture absorbing) materials can be used as relative-humidity sensors. Such materials absorb or lose moisture until a balance is reached with the surrounding air. A change in material moisture content causes a dimensional change, and this change can be used as an input signal to a controller. Commonly used materials include:
- Human hair
- Wood
- Biwood combinations similar in action to a bimetallic temperature sensor
- Organic films
- Some fabrics, especially certain synthetic fabrics
All these have the drawbacks of slow response and large hysteresis effects. Accuracy also tends to be questionable unless they are frequently calibrated. Field calibration of humidity sensors is difficult.
Humidity is read in rh or relative humidity. To obtain the rh, it is necessary to use two thermometers. One thermometer is a dry bulb, the other is a wet bulb. The device used to measure rh is the sling psychrometer. It has two glass-stem thermometers. The wet bulb thermometer is moistened by a wick attached to the bulb. As the dual thermometers are whirled, air passes over them. The dry and wet bulb temperatures are recorded. Relative humidity is determined by:
- Graphs
- Slide rules
- Similar devices
Thin-film sensors are now available, which use an absorbent deposited on a silicon substrate such that the resistance or capacitance varies with relative humidity. They are quite accurate in the range of ±3 to 5 percent. They also have low maintenance requirements.
Stationary Psychrometers Stationary psychrometers take the same measurements as sling psychrometers. They do not move. However, they use a blower or fan to move the air over the thermometer bulbs.
For approximate rh readings, there are metered de- vices. They are used on desks and walls. They are not accurate enough to be used in engineering work
Humidistats, which are humidity controls, are used to control humidifiers. They operate the same way as thermometers in closing contacts to complete a circuit. They do not use the same sensing element, however.
Moisture Analyzers It is sometimes necessary to know the percentage of water in a refrigerant. The water vapor or moisture is measured in parts per million. The necessary measuring instrument is still used primarily in the laboratory. Instruments for measuring humidity are not used here.
Btu Meters The Btu is used to indicate the amount of heat present. Meters are especially designed to indicate the Btu in a chilled water line, a hot water line, or a natural gas line. Specially designed, they are used by skilled laboratory personnel at present.
Vibration and Sound Meters
More cities are now prohibiting conditioning units that make too much noise. In most cases, vibration is the main problem. However, it is not an easy task to locate the source of vibration. However, special meters have been designed to aid in the search for vibration noise.
Portable noise meters are available. The dB, or decibel, is the unit for the measurement of sound. There are a couple of bands on the noise meters. The dB-A scale corresponds roughly to the human hearing range. Other scales are available for special applications.
More emphasis is now being placed on noise levels in factories, offices, and schools. The Occupational Safety and Hazards Act (OSHA) lays down strict guidelines regarding noise levels. There are penalties for noncompliance. Thus, it will be necessary for all new and previously installed units to be checked for noise.
High-velocity air systems—used in large buildings— are engineered to reduce noise to levels set by the OSHA. For example, there are chambers to lower the noise in the ducts. Air engineers are constantly working on high-velocity systems to try to solve some of the problems associated with them.
SERVICE TOOLS
Service personnel use some special devices to help them with repair jobs in the field. One of them is the chaser kit. See Fig. 1-49. It is used for cleaning partially plugged capillary tubes. The unit includes 10 spools of lead alloy wire. These wires can be used as chasers for the 10 most popular sizes of capillary tubes. In addition to the wire, a cap tube gage, a set of sizing tools, and a combination file/reamer are included in the metal case. This kit is used in conjunction with the Cap- Check. The Cap-Check is a portable, self-contained hydraulic power unit with auxiliary equipment especially adapted to cleansing refrigeration capillary tubes. See Fig. 1-50. A small plug of wire from the chaser kit is inserted into the capillary tube. The wire is a few thousandths of an inch smaller than the internal diameter of
the capillary tube. This wire is pushed like a piston through the capillary tube with hydraulic pressure from the Cap-Check. A 0 to 5000 psi gage shows pressure buildup if the capillary tube is restricted. It also shows when the chaser has passed through the tube. A trigger- operated gage shutoff is provided so the gage will not be damaged if pressure greater than 5000 psi is desired. When the piston stops against a partial restriction, high-velocity oil is directed around the piston and against the wall, washing the restriction away and allowing the wire to move through the tube. The lead wire eventually ends up in the bottom of the evaporator, where it remains. The capillary tube is then as clean as when it was originally installed.
A 30 in. high-pressure hydraulic hose with a 1/4 in. Society of Automotive Engineers (SAE) male flare outlet connects the cap tube to the Cap-Check for simple handling. An adapter comes with the Cap-Check for simple handling. Another adapter comes with the unit to connect the cap tube directly to the hose outlet without a flared fitting.
Fig. 1-49 Cap-Check chaser kit. This is a means to clean partially plugged capillary tubes. It has 10 spools of lead alloy wire. These wires can be used as a chaser for the 10 most popular sizes of cap tubes. A cap tube gage, set of sizing tools, and a combination file/reamer are included in the kit.
Fig. 1-50 Cap-Check is a portable self-contained hydraulic power unit with auxiliary equipment that is especially adapted to cleaning refrigeration capillary tubes. It is hand operated.
The Cap-Gage is a capillary tube gage. It has 10 stainless steel gages to measure the most popular sizes of capillary tubes. See Fig. 1-51.
More up to date tools and test equipment are shown in the Appendices. Go online to find the latest available tools and instruments. One source for tools and test equipment is yellowjacket.com or the Ritchie Engineering Company in Minnesota. Another is Mas- tercool.com in New Jersey.
SPECIAL TOOLS
Eventually, almost every refrigerant-charging job turns into a vapor-charging job. Unless the compressor is turned on, liquid can be charged into the high side only so long before the system and cylinder pressures be- come unfavorable. Once that happens, all refrigerant must be taken in the low side in the form of vapor.
Vapor charging is much slower than liquid charging. To create a vapor inside the refrigerant cylinder, the liquid refrigerant must be boiling. Boiling refrigerant absorbs heat. This is the principle on which refrigeration operates.
The boiling refrigerant absorbs heat from the refrigerant surrounding it in the cylinder. The net effect is that the cylinder temperature begins to drop soon after you begin charging with vapor. As the temperature drops, the remaining refrigerant will not vaporize as readily. Charging will be slower.
To speed charging, service personnel add heat to the cylinder by immersing part of it in hot water. The cylinder temperature rises. The boiling refrigerant be- comes vigorous and charging returns to a rapid rate. It is not long, though, before all the heat has been taken from the water and more hot water must be added.
The Vizi-Vapr is an example of how a device can remove liquid from a cylinder and apply it to the system in the form of a vapor. See Fig. 1-52. No heat is required. This eliminates the hazards of using a torch and hot water. The change from a liquid to a gas or vapor
Fig. 1-51 The Cap-Gage is a pocketknife-type cap tube gage with 10 stainless steel gages to measure the most popular sizes of cap tubes. (Thermal Engineering)
Fig. 1-52 The Vizi-Vapr is a device that allows rapid charging of a compressor with- out heating the cylinder of refrigerant. (Thermal Engineering)
takes place in the Vizi-Vapr. It restricts the charging line between the cylinder and compressor. This restriction is much like an expansion valve in that it maintains high cylinder pressure behind it to hold the refrigerant as a liquid.
However, it has a large pressure drop across it to start evaporation. Heat required to vaporize refrigerant is taken from the air surrounding the unit, not from the remaining refrigerant. This produces a dense, saturated vapor.
The amount of restriction in the unit is very critical. Too much restriction will slow charging consider- ably. It also will allow liquid to go through and cause liquid slugging in the compressor. The restriction set- ting is different for each size system, for different types of refrigerants and even for different ambient temperatures.
