1. Hydronic Heating North Seattle Community College HVAC Program
Instructor – Mark T. Weber, M.Ed.
Hydronic - 1

2. Objectives After studying this chapter, you should be able to:
Describe a basic hydronic heating system
Describe reasons for a hydronic system to have more than one zone
List four heat sources commonly used in hydronic heating systems
Explain the difference between a wet-base and a dry-base boiler 2 2

3. Objectives (cont’d.)‏
State the reason a boiler is constructed in sections or tubes
Discuss the reasons why air should be eliminated from hydronic heating systems
Explain the effects air has on a cast-iron or steel boiler
Describe the function of the air cushion or expansion tank 3 3

4. Objectives (cont’d.)‏
Explain the operation of circular pumps as they apply to hydronic heating systems
Describe the importance of the “point of no pressure change”
Describe the purpose of limit controls and low-water cut-off devices
State the purpose of a pressure relief valve
State the purpose of a zone valve and list the various types available 4 4

5. Objectives (cont’d.)‏
Explain how “outdoor reset” can be used to increase system efficiency
Sketch a series loop hydronic heating system and a one-pipe hydronic heating system
Explain the function of the diverter tee
Explain the differences between a two-pipe direct-return and a two-pipe reverse-return hydronic heating system 5 5

6. Objectives (cont’d.)‏
Explain the application that requires the use of a balancing valve
List benefits of primary-secondary pumping
Describe the operation and function of mixing valves
Describe the differences between radiant and conventional hydronic heating systems
List three common types of radiant heating system installations 6 6

7. Objectives (cont’d.)‏
Describe a tankless domestic hot water heater used with a hydronic space-heating system
List preventative maintenance procedures for hydronic heating
Describe the difference between passive and active solar systems
Describe the declination angle and the effect it has on the sun's radiation during winter and summer 7 7

8. Objectives (cont’d.)‏
List the typical components in a liquid-based solar system and describe their function
Describe the operation of a solar domestic hot water system
Describe a swimming pool solar-heating system 8 8

9. Introduction to Hydronic Heating
Water or steam carries heat through a piping arrangement to the areas being heated
Terminal units are located in the heated spaces
Systems can be designed to handle multiple zones
Water is heated at the boiler (gas, oil, or electric)‏

10. Introduction to Hydronic Heating (cont'd.)‏
Boiler cycles on and off to maintain temperature
Water is circulated through the system with pumps
Figure 33–1 A four-zone hydronic heating system.

11. The Heat Source
Boiler: appliance that heats water using oil, gas, or electricity as a heat source
Some boilers can use more than one source
Can supply water at various temperatures, but most common is 180°F
Cast-iron boilers are the most commonly found in residential applications
Steel boiler: water being heated surrounds steel tubes carrying combustion gases

12. The Heat Source (cont'd.)‏
Copper water-tube boiler: low mass boiler, smaller and with lower capacity than cast-iron or steel but efficient
The geothermal heat pump transfers heat from the earth to a water/water-antifreeze mixture and can heat water to 130°F

13. The Basic Hydronic System
Expansion tank
Water expands when heated, so expansion tanks accommodate added volume to prevent excess pressure
Standard expansion tank is a large tank located above the boiler
Diaphragm-type expansion tanks have two sections separated by a semi-permeable rubber membrane
One side contains pressurized air; other is open to water circuit

14. The Basic Hydronic System (cont'd.)‏
Figure 33–15 Cutaway of a diaphragm-type expansion tank. Photo by Eugene Silberstein
Figure 33–16 Expansion tank data tag. Photo by Eugene Silberstein

15. The Basic Hydronic System (cont'd.)‏
Calculate actual pressure required on the air side of a diaphragm-type expansion tank:

16. The Basic Hydronic System (cont'd.)‏
Circulator/centrifugal pumps
Force hot water from heat source through piping to heat transfer units and back to the boiler using centrifugal force
Made up of a motor, a linkage, and an impeller
Figure 33–18 When the impeller is rotated, it “throws” the water away from the center of the pump and out through the opening. Courtesy Cengage Learning 2013.

17. The Point of No Pressure Change
Point in the system where the pressure, no matter what the system is doing, remains the same
Provides a reference point for system evaluation and a location for multiple system-component connections
Desired connection point for inlet of the circulator pump, inlet of the expansion tank, air separator, air vent, and outlet of the pressure-reducing (water-regulating) valve

18. Other Hydronic System Components
Air separator and air scoop
Air is one of the biggest enemies of a hot water hydronic heating system
Air separator separates air from water using collision and adhesion
Directional air scoops separate and remove air on horizontal stretches of pipe

19. Other Hydronic System Components
Air vent removes air from system
Can be manually operated or automatic
Temperature-limiting control (aquastat) maintains water temperature in system

20. Other Hydronic System Components (cont'd.)‏
Figure 33–30 Wire screen in the air separator.
Photo by Eugene
Silberstein

21. Other Hydronic System Components (cont'd.)‏
High-limit control shuts own the heat source if boiler water gets too hot
Water-regulating valve (pressure-reducing valve) reduces pressure of water entering the boiler to desired level
Pressure relief valve discharges excess water when expansion creates pressure
Set to relieve at or below maximum working pressure of the low-pressure boiler (30 psig)‏

22. Other Hydronic System Components (cont'd.)‏
Figure 33–41 A low-water cut-off.
Photo by Eugene Silbersteinn

23. Other Hydronic System Components (cont'd.)‏
Low-water cut-off deenergizes system if level of water in system drops below desired level
Zone valves are thermostatically controlled valves that control water flow to the various zones in the system
May be gear-motor or heat-motor operated, and can often be opened manually
Available in two-port and three-port varieties

24. Other Hydronic System Components (cont'd.)‏
Balancing valves ensure resistance to water flow is the same in all flow paths
Resistance of water flowing in system causes friction
Valves are installed in each circuit branch
Pressure differential bypass valve relieves noise and pressure from closing multiple zone valves in two-port systems
Opens incrementally as valves close

25. Other Hydronic System Components (cont'd.)‏
Flow control valve prevents water from flowing through wrong heating loop (ghost flow)‏
Outdoor reset control senses outdoor ambient temperature and adjusts the water temperature in the boiler
Thermostatic radiator valves are a common method for controlling temperature in each of multiple zones

26. Figure 33–51 Residential outdoor reset control curve
Figure 33–51 Residential outdoor reset control curve. Courtesy Cengage Learning 2013

27. Other Hydronic System Components (cont'd.)‏
Finned-tube baseboard units are common terminal heating units
Heated water flows through piping, transferring heat to fins
Air passes over hot fins and rises by convection
Sections are rated in Btu per linear foot (Btuh/ft), determined by temperature and water flow rate

28. High-Temperature Hydronic Piping Systems‏
Consist of previously discussed components connected together
The series loop system
Most common hydronic system because of low installation costs
Like a series electric circuit, terminal units are piped so outlet of one heat emitter is inlet of next
Main drawback is that individual temperature control for each area being heated is impossible and each terminal unit is cooler than last

29. High-Temperature Hydronic Piping Systems‏ (cont'd.)
Determine amount of water flow with this formula:

30. High-Temperature Hydronic Piping Systems (cont'd.)‏
One-pipe system
One main piping loop extends around the occupied space and connects outlet of boiler back to boiler return
Each terminal unit connects to main loop with two tees, which may be designed for use on a one-pipe system
Proper operation relies on proper ratios of resistance between terminal unit branch and resistance to flow in pipe between the tees

31. High-Temperature Hydronic Piping Systems (cont'd.)‏
Factors to consider in laying out, evaluating, or installing a one-pipe system:
Length of the terminal branch circuit, distance between the tees, size of piping in branch circuit and between the tees, and location of the terminal unit with respect to the main loop
Diverter or Monoflo tees are special tees for one-pipe systems, designed to increase resistance in the main loop pipe section between the two tees so that more water will be directed through the terminal heating units

32. High-Temperature Hydronic Piping Systems (cont'd.)‏
The two-pipe direct-return system
Uses one pipe to carry water to the terminal units and another to carry water from the terminal units back to the boiler
Terminal unit closest to the boiler will have the shortest piping run (lowest resistance) while the unit farthest from the boiler will have the longest

33. High-Temperature Hydronic Piping Systems (cont'd.)‏
The two-pipe reverse-return system
First terminal unit to be supplied with water is the last to return water to the boiler
Unit with shortest supply pipe will have longest return pipe and vice versa

34. High-Temperature Hydronic Piping Systems (cont'd.)‏
Primary-secondary pumping
Involves at least two separate piping circuits between the boiler and terminal unit circuits
One circuit path flows from the boiler supply back to the boiler return
The secondary circuit(s) is/are connected to the main/primary circuit and share a portion of piping
Uses standard tees
Mixing valves combine two water streams of different temperatures

35. High-Temperature Hydronic Piping Systems (cont'd.)‏
One of many benefits of primary-secondary pumping is that each loop can be used to supply water at different temperatures to the terminal units in that loop
Primary-secondary systems do not have expansion tanks in each of the secondary loops because the common piping between the primary and secondary loops serves as the expansion tank for that loop

36. Radiant, Low Temperature Hydronic Piping Systems
Rely on heating the shell of the structure as opposed to the air in that structure
The human body acts as a radiator
Under normal conditions, the body produces about 500 Btu/h but only requires 100 Btu/h to remain alive; typically a room temperature of 68°F allows us to shed the extra 400 Btu/h comfortably
The area close to the ceiling can be cooler and the floor should be warmer

37. Radiant, Low Temperature Hydronic Piping Systems (cont'd.)‏
Main differences between radiant heating and conventional hydronic systems:
Radiant heating systems are nearly invisible compared to conventional hydronic systems
Different piping materials
Radiant systems often use polyethylene (PEX) tubing instead of copper piping
Water temperature in radiant heating systems considerably lower than in conventional hydronic systems (avg. of 110°F)

38. Radiant, Low Temperature Hydronic Piping Systems (cont'd.)‏
Heat sources for radiant heating systems
Geothermal heat pump system
Use a buffer tank
Copper-tube, low-mass boiler
A buffer tank is still a good idea
Direct piping
Boiler must be designed to handle potentially low temperature of water returning to the tank or provide a means to keep return-water temperature high enough to prevent flue-gas condensation

39. Radiant, Low Temperature Hydronic Piping Systems (cont'd.)‏
Radiant heat piping applications
Slab on grade
Popular for new construction applications
Spacing of PEX tubes in fresh concrete depends on depth below concrete surface, size of tubes, type of floor, and location of tubes with respect to the outside walls of the structure
Place insulation and a vapor barrier below the concrete slab to prevent losing heat to ground

40. Radiant, Low Temperature Hydronic Piping Systems (cont'd.)‏
Thin slab
Common when there is an existing floor in place
1.5-2” slab of concrete poured over tubing; completely cover PEX tubing with at least ¾” of concrete
Dry applications
Staple the tubing to the bottom of the flooring material (staple-up job)‏
Keep staples closely spaced so that tubing is in loose contact with floor for effective heat transfer
Another concrete-free option is aluminum fins attached to PEX tubing fed through floor joists

41. Radiant, Low Temperature Hydronic Piping Systems (cont'd.)‏
Many different piping arrangements can be used with radiant heating, including:
Direct piping is the simplest configuration
Best to use a buffer tank with a boiler
Manually set mixing valves do not respond to changes in water temperature or flow rate
Thermostatic mixing valves adjust internal settings to supply water at the desired temperature; prevents flue gas condensation

42. Combination (High- and Low-Temperature) Piping Systems
In the case where a structure has both high and low temperature heating circuits, the same boiler can be used to serve both applications using a primary-secondary pumping arrangement

43. Tankless Domestic Hot Water Heaters
Most oil and gas fired hot water heating boilers can be furnished with a domestic hot water heater consisting of a coil inserted into the boiler containing the domestic hot water, heating it quickly
Eliminates the need for a storage tank
An efficient way to produce hot water

44. Solar Heating as a Supplemental Heat Source
It is estimated that two weeks of solar energy is equal to all known deposits of coal, gas, or oil
The challenge is to better harness and use this energy, for example to collect, store, and distribute solar heat

45. Passive Solar Design
Uses nonmoving parts of a building or structure to help provide heat or cooling or eliminate parts of a building causing inefficient heating or cooling
Examples: placement of windows, greenhouses, roof overhangs, etc.
Contrast with active solar systems that use electrical or mechanical devices to help collect, store, and distribute the sun's energy

46. Direct and Diffuse Radiation
Only about % of the sun's energy reaches the earth as direct radiation
Energy that is reflected into space or scattered by absorption in moisture and pollutants is called diffuse radiation

47. Solar Constant and Declination Angle
The rate of solar energy reaching earth's atmosphere is the same at all times
Solar constant: 429 Btu/ft²/h
Intensity of solar energy reaching the northern/southern atmospheres varies because of declination angle: 23.5°
Radiation also varies because of distance and angle of rays with regard to a particular place

48. Active Solar Design
Uses collectors, storage systems, distribution devices such as pumps and fans, and control systems
Liquid solar forced air space-heating systems
Drain-down systems used in areas where water to, from, and in collectors would freeze if left in the system
Circulator pumps move water from storage
Alternative uses closed-collector piping with antifreeze solution

49. Active Solar Design (cont'd.)‏
Liquid collection/water storage/auxiliary conventional hot water boiler
Liquid-based solar collector may be paired with a hot water finned-tube convector heating furnace
System uses the auxiliary boiler when the storage water is not hot enough, or may be designed as two separate systems in parallel so that both can operate at once

50. Solar Radiant Heat
Water or antifreeze is piped through a collector system
Heating coils may be imbedded in concrete in the floor or plaster in ceilings or walls
Normal surface temperature is 85°F for floor heating or 120°F for wall or ceiling panels

51. Solar-Heated Domestic Hot Water
Many solar systems are installed specifically to heat or assist in heating domestic hot water
Heated collector water or antifreeze is pumped into the heat exchanger to provide heat to the water in the tank
Toxic antifreeze must be separate from water
Flat-plate liquid solar collectors use one or two panels of glass, an absorber plate, and black paint to absorb maximum heat

52. Solar Pool Heating
Many use the pump that circulates pool water through the filter
Pool water is pumped through filtering devices, then diverted to solar collectors to be heated before flowing back to the pool
When pool reaches desired temperature level, water bypasses collectors and returns directly to the pool

53. Summary
Hydronic systems carry heated water or steam to remote locations via piping arrangements
Boiler cycles on and off to maintain the desired water temperature in the system
Component parts include the air separator, air vent, limit control, circulator, water regulating valve, and flow control valve 53 53

54. Summary (cont’d.)‏
The ASME requires the installation of a pressure relief valve on all hot water boilers
Forced air hot water unit heaters are used in commercial and industrial applications and use fans to move air across the heat exchanger surface 54 54

55. Summary (cont’d.)‏
Common hydronic piping arrangements include the series loop system, one-pipe system, two-pipe reverse return and two-pipe direct return
The one-pipe system uses diverter tees to balance water flow through all terminal units 55 55

56. Summary (cont’d.)‏
Liquid solar forced air space-heating systems may use drain-down or closed- collector piping system
Liquid solar space-heating systems may be combined with many types of conventional heating systems
Solar heating may be used to heat domestic hot water and swimming pools 56 56

57. For more information please contact Mark T. Weber At
North Seattle Community College