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Danica’s Steamfitter III Review > High Temp Hot Water Systems > Flashcards

High Temp Hot Water Systems Flashcards

1
Q

At what temperature does a high temperature hot water system start?

A

177°C

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2
Q

What is the range in temperature for a high temperature hot water system?

A

177°C to 232°C

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3
Q

What temperatures do medium temperature Hot water systems Generally operate at?

A

121°C to 177°C

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4
Q

What specifications are high temperature hot water boiler set to?

A

ASME section one

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5
Q

What type of boiler is used for high temperature Hot water service?

A

Water tube

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6
Q

Where is the return water directed in a high temperature Hot water system?

A

Below the boiler waterline

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7
Q

What does the feed water pass through upon entering the boiler?

A

Expansion drum.

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8
Q

What are the three advantages of using a steam boiler for high temperature hot water systems?

A
  1. Existing steam boilers can be readily converted.
  2. You can change the steam and hot water ratios to suit demands.
  3. Temporary loss of pressure doesn’t affect the system so long as the water level is maintained.
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9
Q

Are threaded fittings on HTHW systems permitted?

A

No

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10
Q

How do HTHW systems deal with system expansion, and contraction?

A

Through the use of steam for pressurizing, the expansion drum or the use of a nitrogen or steam pressured cascade heater, which functions as an expansion drum

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11
Q

Is a nitrogen padded expansion drum installed horizontally, or vertically and why?

A

A nitrogen padded expansion drum is installed vertically to decrease the interface area between the gas and the water

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12
Q

When a steam pad is used to pressurize the system is the expansion drum set horizontally, or vertically and why?

A

Horizontally and elevated well above the circulating pumps to prevent cavitation.

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13
Q

What are some advantages of an HTHW system over a steam system?

A
  1. Less water treatment is required.
  2. They have smaller boiler feed pumps.
  3. Piping elevation changes are not a problem as no traps are required however, events are required at the Highpoints.
  4. There is less internal corrosion because less makeup water is required.
  5. Larger temp differentials allow for use of smaller heat units and smaller pipe sizes.
  6. Historically they have lower maintenance costs.
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14
Q

What are the disadvantages of HTHW over steam systems?

A
  1. The system takes longer to heat up, especially from cold start after shut down.
  2. Standby pumps are required.
  3. Circulating pumps must operate continuously.
  4. Sudden leaks will drop pressure which result in the formation of flash steam. Flash steam can cause water hammer, and cavitation in other parts of the system.
  5. Pump selection and trim are more difficult. High temperature water is classified as a hard to hold fluid.
  6. Pipe sizing, and design layout are much more critical to prevent noise and cavitation.
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15
Q

How is circulation accomplished in an HTHW generator?

A

Thermal currents of flow from the circulating pumps. Heat absorbing tubes are piped to upflow water and downcomer are insulated to protect from hot gases in the unit.

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16
Q

Which gas is preferred to pressurize the expansion drum?

A

Nitrogen

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17
Q

Why is compressed air not used to pressurize the expansion drum?

A

Oxygen would adversely affect the system components

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18
Q

Does water or steam have more thermal capacity by volume?

A

Water

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19
Q

Why is a manual vent required on an HTHW generator?

A

To vent air

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20
Q

What is the minimum designation and grade of pipe used for an HTHW system?

A

ASTM designation a – 53, grade a, no less than schedule 40 pipe.

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21
Q

What temperature are HTHW systems usually limited to?

A

232°C

22
Q

When are common problems typically found in the HTHW systems operation?

A

Within the first two heating seasons

23
Q

Service problems in an HTHW system arise as a result of what?

A
  1. Design problems.
  2. Maintenance procedure not being followed.
  3. Changes being made to system that were not foreseen at the time of its conception.
24
Q

What are the symptoms of an overloaded boiler?

A

Accumulated sediment buildup, which will cause water circulation problems, or in severe cases, the fracturing and sagging of the tubes in the boiler.

25
Q

What would cause a boiler to be overloaded?

A

A lack of balance between boilers in the same plant. where supply and return headers in the HW boiler house are not interconnected in such a way that all boilers are being equally used, balancing of these circuits should be considered.

26
Q

What problems can arise using steam instead of nitrogen in the system for pressurizing?

A

Flashing in the system, which likely occurs at the Highpoint in the system farthest away from the boiler. Cavitations at pumps that lead to steam flashing can result in the failure of mechanical seals and problems with the stuffing box. This could lead to insufficient mixing of supply and return on the pump suction side. If cold water is introduced on the suction side of the pump, it could lead to water hammer that can severely damage piping valves and controls.

27
Q

What should we use to avoid large pressure drops in the boiler?

A

Additional circulating pumps can provide the standby protection that is needed. For example, where two boilers are tied together, The use of three circulating pumps should be incorporated. This provides one circulating pump for each boiler and an additional pump that can be used on standby.

28
Q

What are the four maintenance requirements of HTHW systems?

A

keep accurate readings of CO2, O2,and fuel consumption, water treatment to maintain the proper pH, adequate filtering of the draft fans, and strainer maintenance.

29
Q

Failure to keep accurate readings of the CO2, O2, and fuel consumption can lead to which problem?

A

The boiler is not being balanced in operation. Problems with accurate readings are a result of calibration not performed on recording instruments that ensure the proper operation of the boilers.

30
Q

Failure to meet water treatment requirements causes which issues?

A

The proper pH of the water must be maintained. Poor practises in this area lead to scale and corrosion, erosion, and other forms of deterioration of piping valves and controls.

31
Q

What occurs when there is a failure to provide adequate filtering?

A

Vibration problems in the system are the result of induced and forced draft fans having inadequate filtering of soot or fly ash. Soot can rapidly build up on fans.

32
Q

Failure to maintain the strainers causes what problems in a HTHW system?

A

Problems with pump seals, specifically the mechanical style (where clogging has prevented the seal from returning to its proper position). The proper cleaning of strainers on the suction side of the pump will avoid this.

33
Q

What can threaded joints cause in an HTHW system?

A

Piping that is threaded on lines 1 1/4” or smaller result in weeping and flashing in many cases regardless of the threading procedure followed. to correct this problem the piping has to be welded to control the energy losses.

34
Q

What can occur if expansion and contraction is not taken into account for on an HTHW system after installation?

A

In the event that expansion and contraction is not properly allowed for damage to pipes fittings, valves, and controls, will occur as well as damage to the building as piping expands, and eventually will push through the walls. Another common problem is the installation of undersize bolt anchors resulting in the bolts breaking.

35
Q

Define reactive maintenance

A

Paying attention to equipment only when it breaks down and requires repair.

36
Q

Define preventative maintenance

A

Preventative maintenance is scheduled on a regular basis and can include tasks such as monthly lubrication and recalibrations performed, perhaps quarterly or semi annually

37
Q

Define predictive maintenance

A

Predictive maintenance occurs based on the current condition of equipment, and is often a response to what was observed at the preventative stage of the maintenance program.

38
Q

Define proactive maintenance

A

Proactive maintenance seeks to modify such things as procedures and equipment to ensure continued or improved. Performance were breakdown, is not consideration this could include altering the frequency of maintenance tasks.

39
Q

The American National Standards Institute (ANSI), previously known as the American standards association (ASA), the American Institute of steel construction (AISC) and the American welding society (AWS) were formed in between which years?
A-1902-1911
B-1911-1912
C-1911-1921

A

C-1911-1921

40
Q

What two gases are used to pressurized a high temperature hot water system?

A

Nitrogen and steam

41
Q

What type of event is used on an HTHW system?

A

Manual

42
Q

How does the HTHW boiler differ from an HP steam boiler?

A

The boiler nozzle

43
Q

How is low pressure steam created in an HTHW system?

A

Through use of an immersion generator

44
Q

Why is the system pressure maintained above saturation temperature of water?

A

So the high temperature hot water will not flash

45
Q

Why can smaller diameter lines be used for HTHW systems?

A

HTHW has a higher thermal capacity than steam

46
Q

Why is the expansion drum elevated when using a steam pad for pressurization?

A

To prevent pump cavitation

47
Q

What section of the ASME code are HTHW systems designed in accordance with?

A

ASME section one

48
Q

What is one similarity in steam boiler design used for HTHW installation that is shared with other types of high-pressure steam boilers?
A. They are fire tube boilers.
B. The boilers are sectional and construction.
C. There is no steam drum.
D. They are usually of a welded construction.

A

D. They are usually of a welded construction.

49
Q

How is the circulation of water achieved on a high temperature hot water generator?

A

Circulation is achieved by a combination of thermal currents and flow from the systems circulating pumps

50
Q

The suction discharge piping on and expansion drum is sized according to what?

A

The water velocity.

Danica’s Steamfitter III Review (12 decks)

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