Heating I Section#2 Hot Water Boiler Quiz#6

This study session deals with the sequence of operation of boilers, tankless coils, high-efficiency boilers, lifespans of various boilers and combination systems.

The estimated completion time for this study session is sixty minutes.

Objectives
At the end of this study session, you should be able to:

• List the four problems found with tankless coils.
• List and briefly describe the steps in the sequence of operation.
• List the problems found with high-efficiency boilers.
• List the problems found with combination systems.
• Understand how long different boilers last.
• Understand how to use a general rule to determine the adequacy of the boiler capacity.

Describe the sequence of operation for a system where the boiler cools when the system is at rest. Assume that the circulating pump runs continuously.

1. The thermostat calls for heat

2. The burner comes on

3. The water in the boiler is heated

4. The circulator carries the hot water through the pipes to the radiators

5. The radiators heat the rooms

6. The thermostat is satisfied 

7. The burner turns off

8. The water cools

9. The pump continues to run

Explain how a side-arm heater is different from the tankless coil.

A side-arm heater is mounted outside the boiler. Its function is identical to a tankless coil.

List six conditions that could be found with high efficiency boilers. Include one problem which is unique to high efficiency boilers

1. Cabinet problems
2. Fuel supply and burner problems
3. Combustion air and venting problems
4. Ignition problems Heat exchanger problems
5. Safety and operating control problems
6. Induced- and forced-draft fan problems
7. Condensate handling problems
8. Distribution problems
9. Inadequate waterflow through boiler - unique to high efficiency boilers
10. Noise - unique to high efficiency boilers (and high efficiency furnaces)

What are some of the design and operating challenges of high-efficiency boilers?

1. High efficiency boilers are expensive.
2. Condensation is corrosive.
3. Complex systems lead to high maintenance costs and poor reliability.
4. High efficiency boilers may not be a good match for old piping and radiator systems.
5. The radiator temperatures may be too low.
6. The return water temperature is usually too high to encourage condensation in the products of combustion.
7. The small volume boilers may overheat if the water flow through them is not adequate. Short cycling can be a problem.

What are three possible advantages of high efficiency boilers?

1. No chimney needed
2. Lower fuel costs from increased efficiency
3. Direct venting

What are two improvements which can be made to a boiler to make it a mid-efficiency boiler?

1. Vent damper, or induced-draft fan
2. Electrical ignition.

What is the difference between a combination system and a tankless coil system?

A combination system uses the domestic water heater to heat both the domestic water and living space. A tankless coil uses the boiler from a hydronic heating system to heat the domestic water.

Why is a tankless coil water heater called an indirect water heater?

The water in the tankless coil is heated by boiler water, rather than a flame.

Why would you have a mixing valve on a tankless coil heater?

To reduce the temperature of the domestic water below the boiler water temperature to prevent scalding.

Boilers with tankless coil domestic water heaters are inefficient because:

The boiler needs to stay on all summer*