In the illustrated single zone HVAC system,...

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Question 1 of 2066636eee28f7522a1c51eba1

In the illustrated single zone HVAC system, what prevents the simultaneous flow of steam through the preheat coil and flow of chilled water through the cooling coil? Illustration RA-0009

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Question 1 of 20

66636eee28f7522a1c51eba1

In the illustrated single zone HVAC system, what prevents the simultaneous flow of steam through the preheat coil and flow of chilled water through the cooling coil? Illustration RA-0009

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🔍 Key Concepts

• Single-zone HVAC control sequence – how heating (steam preheat) and cooling (chilled water coil) are staged so they don’t fight each other • Supply duct thermostat setpoints – how the heating setpoint must relate to the cooling coil’s design off-coil temperature to avoid simultaneous heating and cooling • Purpose of the preheat coil (protect coils / temper cold air) versus the cooling coil (reduce temperature and humidity)

💭 Think About

• Imagine a typical design off-coil temperature for the cooling coil (for example, around 55°F). If the steam preheat thermostat were set ABOVE that, what would the heating valve try to do whenever the system is cooling? • If the steam preheat thermostat were set BELOW the cooling off-coil temperature, what would the preheat valve be doing while the cooling coil is operating at its design off-coil temperature? • Why would an engineer want a “deadband” between heating and cooling, instead of having both coils operating at the same time?

✅ Before You Answer

• Identify where in the duct the thermostat that controls steam flow is located relative to the coils in the illustration. • Compare the steam preheat thermostat setting to the design off-coil temperature of the cooling coil and decide which relationship (higher, equal, or lower) prevents overlapping operation. • Confirm whether the control strategy for this single-zone system is intended to avoid or allow simultaneous heating and cooling for humidity control.

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Question 1 of 2066636eee28f7522a1c51eba1

In the illustrated single zone HVAC system, what prevents the simultaneous flow of steam through the preheat coil and flow of chilled water through the cooling coil? Illustration RA-0009

Back

Question 1 of 20

66636eee28f7522a1c51eba1

In the illustrated single zone HVAC system, what prevents the simultaneous flow of steam through the preheat coil and flow of chilled water through the cooling coil? Illustration RA-0009

No comments yet

Be the first to share your thoughts!

If the question has a related picture, it will appear here.

🔍 Key Concepts

💭 Think About

✅ Before You Answer

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