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HVACR216 - Hydronics
Hydronic Heating
Hydronic Heating Systems
• Hydronic heating systems rely on circulating
water or steam to deliver heat to the remote
locations where warming of a space is desired.
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Hydronic Heating Systems
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Hydronic Heating Systems
The Heat Source
• Heat energy is transferred from the heat
source (burners) to the water in the boiler.
– There are two different types of boilers on the
market today.
• High mass
• Low mass
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The Heat Source
• Cast iron (high mass) boilers are most
commonly boiler found in residential
applications.
– Residential cast iron boilers typically hold
between 10 - 15 gallons of water.
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Cast iron (high mass) boiler
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Cast iron (high mass) boiler
• The boiler manufacturer supplies us with a booklet
that is sent with the boiler.
• It is important that these instructions are followed
when the boiler is installed.
• This booklet also contains information about
proper boiler maintenance or troubleshooting.
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The Heat Source
• Stainless steel (low mass) boilers are
gaining popularity due to the higher
efficiencies being obtained today by many
different manufacturers.
– Low mass boilers hold between 4 - 7 gallons
of water.
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Low mass boiler
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Hydronic controls
• Thermostat
– The heating thermostat, whether it is a modern
digital, snap action or mercury bulb type, is a
close on temperature drop device.
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Thermostat types
• Digital
Snap action Mercury bulb
Hydronic controls
• Aquastat
– The Aquastat is a temperature-sensing
switch that is responsible for cycling
the boiler on and off to keep the water
in the boiler close to the desired
temperature.
– It may be strapped onto a pipe or
immersed in the water via a well.
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Aquastat types
• Immersion
Strap-on
Triple
Low Water Cutoff
• The Low Water Cutoff is responsible for deenergizing the combustion operation in the event
the water level in the system falls below the
desired level established by the manufacturer.
• The Low Water Cutoff is a safety device that
code officials require to be installed on all
hydronic systems.
• The Low Water Cutoff can be a stand alone
device or a built in part to the Aquastat.
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Low Water Cutoff
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High limit switch
• Manual reset high limit switches are required
in light commercial applications.
Circulator Pumps
• The circulator pump is used to move water
throughout the hydronic system.
• The circulator pump is also called a
centrifugal pump.
• The centrifugal pump is made up of a motor,
a linkage and an impeller.
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Circulator pump styles and brands
• Taco 007
Taco 110
Grundfoss
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Circulator location
• Early circulators were large and heavy. The
easiest place to mount them was on the return
piping close to the boiler.
• Modern locations for a circulator is on the supply
piping just beyond the air eliminator and the
expansion tank.
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Pump control panels
• Circulator pump panels (switching relays)
control the operation of multiple pumps
(zones) at one time.
– A thermostat located in the space to be heated
calls for heat and the zone panel turns on the
correct circulator for that space.
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Taco zoning controls
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Zone valves
• Zone valves are sometimes used to allow
or dis-allow water from flowing through a
system.
• Zone valves are either directly controlled
by a thermostat or a zone panel
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Zone valve brands
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Taco
Honeywell
B&G
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Cut-away picture of a zone valve
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Zone valve panels
• Zone valves can also be controlled by a
panel much like the circulator pumps.
Non-electrical components
• Expansion Tanks
– There are two types of expansion tanks
• Standard expansion tank
– Nothing more than a large tank located
somewhere above the boiler.
• Diaphragm expansion tank
– Divided into two sections separated by a
rubber, semi-permeable membrane.
– One side of the tank contains air and the
other side is open to the water circuit.
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Modern diaphragm expansion tank with air scoop and vent.
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Automatic water feed
• Automatically maintains the preset water
pressure in the system.
• Usually 12-14 psi
Combination Auto Feed and Backflow Preventer
The backflow preventer allows water flow only
in one direction similar to a check valve.
Its very common to see the backflow preventer
and the water feeder together like this.
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Pressure-reducing Valve
• Another name for the water feeder is the
pressure reducing valve.
• The pressure-reducing valve automatically
lowers the pressure of the supply water to the
pressure at which the boiler is designed to
maintain.
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Pressure reducing valve
Pressure Relief Valve
• The pressure relief valve is designed to
open if the pressure in the system
reaches the set point on the valve.
– The is the most important safety
device installed on a hydronic
system.
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Pressure Relief Valve
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Flow-Control Valve
• The flow-control valve controls flow in a
hydronic system.
• The flow control valve is also called a
check valve or flow check.
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Flow-Control Valve types
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Balancing Valve
• Balancing valves are used to even the
water flow through each branch of the
circuit.
• Balancing valves are installed in each
branch of the circuit and are manually
adjusted.
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Balancing Valve