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

To increase system water pressure

Answer

To filter debris from the water

Answer

To balance flow between multiple zones

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

To separate domestic hot water from heating water

Answer

To provide redundancy in case one boiler fails

Answer

To reduce water pressure in high-rise buildings

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

Overheating due to blocked heat exchanger

Answer

Electrical damage from voltage spikes

Answer

Freezing of the heat exchanger in winter

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

To maintain minimum boiler water temperature

Answer

To prevent backflow in the system

Answer

To regulate boiler firing rate

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

PEX tubing cannot handle higher temperatures

Answer

Higher temperatures would cause the concrete to crack

Answer

The pump cannot handle higher temperatures

Question 6

What does 'Delta T' (ΔT) mean in a hydronic heating system?

Accepted Answer

The temperature difference between supply and return water

Answer

The maximum pressure difference between supply and return

Answer

The temperature rise across the boiler only

Answer

The difference between indoor and outdoor design temperatures

Question 7

What is 'hydraulic separation' and which device achieves it?

Accepted Answer

Decoupling boiler flow from distribution flow; low-loss header or hydraulic separator

Answer

Air separation from water; air scoop

Answer

Pressure separation between zones; pressure reducing valve

Answer

Chemical separation of corrosion products; filter separator

Question 8

What is 'cold start' operation in a boiler?

Accepted Answer

Starting a boiler from ambient temperature; causes thermal shock from cold water contacting hot surfaces

Answer

Starting a boiler after power failure; causes pressure spikes

Answer

Operating a boiler in cold weather; reduces efficiency

Answer

Starting a condensing boiler; requires a warm-up period

Question 9

How does a three-way mixing valve work in a hydronic radiant system?

Accepted Answer

It blends hot boiler supply water with cooler return water to produce a lower supply temperature for distribution

Answer

It mixes refrigerant with the heating water

Answer

It separates domestic hot water from heating water

Answer

It automatically adjusts boiler firing rate

Question 10

What problems arise from excessively high water velocity in hydronic piping?

Accepted Answer

High velocity causes erosion-corrosion, noise, and air entrainment

Answer

Higher velocity always improves heat transfer; no problems

Answer

High velocity reduces pressure, causing boiler short cycling

Answer

High velocity improves efficiency by reducing stratification