3rd Period Hydronic Heating Review Flashcards
What are the 2 types of heat exchangers?
High Mass and Low Mass
What are the 2 types of high mass heat exchangers?
Cast iron and fire tube
What are the 2 types of low mass boilers?
Copper tube and steel tube
What are 3 advantages of high mass boilers?
- Stable water temp
- Sections are expandable (cast iron)
- Gravity system, low mass needs flow so can’t be gravity (cast iron)
What are 3 advantages of low mass boilers?
- Quick response time
- Lighter, easier install
- Heat domestic directly (copper tube) tankless
What are 2 precautions regarding high mass boilers?
- High explosive potential
2. 30 psi max (cast iron)
What are 2 precautions regarding low mass boilers?
- Flow is critical
2. Susceptible to thermal shock
What component is required on all
High mass boilers over 400,000 BTU?
Low water cut off
What component is required on all
Low mass boilers over 400,000 BTU?
Flow switch
What is input rating and how do you find it?
Amount of heat energy in the fuel burned by the burner
Located on the rating plate of the appliance
What is output or gross output rating and how do you find it?
Amount of heat energy available at the boiler outlet
Located on the rating plate or manufacturers instructions
Input 100 MBH 95% eff. Output is 95 MBH
What is net rating and how do you find it?
Amount of heat energy available at the heat emission units (rooms)
Gross output x 0.75 = net rating
(75% of gross rating)
Calculate output rating of a 250MBH boiler that is 85% efficient
250,000 BTU x 0.85 = 212,500 BTU/hr
Net rating
212,500 x 0.75 = 159,375 BTU/hr
What is the function of the operating switch on a boiler?
Controls operation of the boiler (controls the burner)
What is the function of a high limit switch?
Set at a higher temperature than the preferred operating temperature and acts as a safety if temp is too high (shuts off the burner)
Where must a low water cut off be located on a high mass boiler?
Above the heat exchanger of the boiler
Series Loop
One pipe system
Temperature reduces after each unit
Flow rate stays the same (balanced)
Limited to one thermostat
Split series loop
One pipe system
Temp. reduced at each unit after split
Flow rate depends on balancing valves
2 thermostats possible
Mono flow system
One pipe system
Temperature reduced at each unit
Flow rate variable at each unit (balancing valve on each)
Multiple zoning possible (can service individual units)
Direct Return
First Supply First Return
Two Pipe System
Supply temp. same at each unit
Flowrate: variable at each unit, short circuit potential (balancing valves required)
Multiple zoning, can service individual units
Reverse Return
First supplied Last returned
Two pipe system
Supply temp. same at each unit
Flowrate: variable at each unit, balanced flow
Multiple zoning, can service individual units
If flowrate or boiler temp increases, what happens to the length of baseboard required?
Less baseboard
If the entering air temp decreases, what happens to the amount of BTU output?
Increase (has to work harder)
BTU = ___ x ___ x ___
500 x 🔺T x gpm
or
gpm = BTU / (500 x 🔺T)
