Heating And Cooling Systems 030203a Flashcards
What is temperature a measure of?
An object’s thermal energy.
What is a BTU (British thermal unit) defined as?
The approximate quantity of heat required to raise the temperature of 1 pound of water by 1 degree Fahrenheit.
Heat is transferred from one object to another by 3 different ways. What are they?
Conduction.
Convection.
Radiation.
The method by which heat is transferred through solids is known as what?
Conduction
Method by which heat is transferred through fluids such as air or water is known as?
Convection.
Heat transfer by electromagnetic wave motion is known as?
Radiation.
What four variables are human comfort dependent on?
Temperature.
Humidity.
Air movement.
Radiation.
What is the term Cold 20 referring to?
When a temperature is set to 20 degrees Celsius but the room still feels cold due to the other variables like air movement, humidity or radiation.
What is one BTU (British thermal unit) equivalent to?
250 calories or 1055 joules.
What is one calorie defined as?
The amount of heat required to raise the temperature of 1 gram of water by 1 degrees Celsius at atmospheric pressure.
What are the four main reasons for using automatic controls?
Comfort, safety, economy and convenience.
How would heat be defined?
A form of energy arising from the random motion and collision of molecules.
Heat always transfers from hotter to cooler.
How is cold defined?
The relative lack of heat.
What are the three types of bimetal temperature sensing devices?
Strip type. (Two strips of dissimilar metals)
Spiral type. (Bimetal strip in the shape of a spiral. Ideal for activating mercury bulb switches.)
Disc type. (Suitable for larger ampacity loads. Also suitable for monitoring the temperature of moving air.)
What are all the types of temperature sensing devices?
Bimetal.
Bellows.
Liquid bulb.
Thermocouple.
Thermopile.
Thermistor.
Resistance Temperature Detector. (RTD).
Pyrometer.
What are liquid bulb temperature sensing devices really good for?
Monitoring the temperature of water and air in a pipe or tank.
What are thermocouples and how much voltage do they generally generate?
Temperature sensor that generates a small voltage in proportion to temperature.
Typically generate a voltage between 26-32 millivolts DC.
What is the device called that has many thermocouples connected in series?
Thermopile or powerpiles.
Voltage can reach as high as 800 mV DC.
What is the a thermistor?
A solid state device in which the resistance of the semiconductor material changes in response to changes in temperature.
What type of temperature sensing device has a negative temperature coefficient?
Thermistors.
As temperature goes up, resistance goes down.
What is the most common type of metal used in resistance temperature detectors and why?
Platinum.
Chemically stable metal that resists corrosion and oxidation in hostile environments. Has a very high melting point.
What temperatures can pyrometers measure?
As high as 4000 degrees Celsius.
Suitable for measuring the temperature in industrial kilns and metal refining furnaces.
What temperature sensing devices are considered as solid-state?
Thermistors.
Resistive temperature devices (RTDs).
Thermocouples.
Thermopiles.
Which temperature sensing device uses the expansion and contraction of ether?
Bellows type.
What are the three types of contacts in a thermostat?
Mercury contacts.
Spring-activated, snap-action exposed contacts.
Glass-enclosed magnet and armature snap-acting contacts.
What component of a thermostat can increase the sensitivity of thermostats?
Anticipators
What are the thermostat wiring terminals and what is each terminal meant for?
Source - R, Rh, Rc
Heating - W
Cooling - Y
Fan - G
Common - C
What are some types of heating systems?
Resistive.
Forced Air.
Hydronic.
Heat pump.
What is the most common type of electric heating system and what is an example of it?
Resistive heating.
Electric baseboard heating.
What type of heating unit can be either passive or forced air?
Resistive heating.
Which device can provide both cooling and heating?
Heat pumps.
Which method of heat transfer does a hydronic heating system utilize?
Convection.
What are thermocouples most often used for?
To prove the existence of a flame.
Used in hot water tanks, furnaces or gas fireplaces.
What are the advantages and disadvantages of thermocouples?
Advantages - simple, durable construction and relatively low cost.
Disadvantages - Slow response time.
What is the expected mV output of a thermocouple when doing a closed circuit test?
25% to 50% of the open circuit mV output.
7.5mV to 15 mV.
What are the tests that you should perform on a thermocouple?
Open-circuit test. (26 to 32 mV)
Closed-circuit test (7.5 to 15 mV)
Response time test.
Dropout point test.
Turn down test (performed by a gas fitter.)
How do you convert Celsius to Fahrenheit?
Temperature x 1.8 + 32
