HVAC Hydronic Heating Systems

Question 1

What is the primary function of an expansion tank in a closed-loop hydronic heating system?

Accepted Answer

To accommodate the volume increase of water as it heats and expands

Answer

As water heats it expands in volume. The expansion tank absorbs this expanded volume, preventing excessive pressure buildup.

Question 2

What is the purpose of a 'primary-secondary' piping configuration?

Accepted Answer

To allow each zone to operate at different temperatures and flow rates without affecting boiler flow

Answer

Primary-secondary piping uses closely spaced tees to hydraulically decouple the boiler loop from distribution loops, allowing independent flow rates.

Question 3

What is 'thermal shock' in a cast iron boiler?

Accepted Answer

Rapid temperature differential causing cracking when cold water hits hot boiler sections

Answer

Thermal shock occurs when cold return water suddenly contacts hot cast iron boiler sections, creating rapid thermal expansion differentials that can crack the cast iron.

Question 4

What is the function of a 'differential pressure bypass valve' in a variable flow hydronic system?

Accepted Answer

To bypass excess water flow when zone valves close off, protecting the pump and boiler

Answer

When zone valves close simultaneously, pressure increases. The differential pressure bypass valve opens to allow excess flow to bypass, maintaining minimum boiler flow.

Question 5

In radiant floor heating, why is water temperature limited to 85-120°F?

Accepted Answer

Floor surface temperatures above ~80°F are uncomfortable for occupants

Answer

Floor surface temperatures above approximately 80-85°F are uncomfortable for standing occupants, so supply water temperature is limited to maintain comfortable floor temperatures.

HVAC Practice Test

HVAC Practice Test

HVAC Hydronic Heating Systems