System Design & Load Calculation Flashcards

What does the 'system balance point' mean in refrigeration system design?

Answer: The operating condition where system capacity exactly matches the refrigeration load

The balance point is where the system's capacity curve intersects the load curve, meaning the equipment removes heat exactly as fast as it enters the space.

Short cycling in a refrigeration system is most likely to result in which design problem?

Answer: A grossly oversized system that satisfies the load too quickly without adequate run time

Short cycling occurs when the system is oversized and satisfies the load too quickly, leading to frequent on/off cycling that reduces efficiency, increases wear, and causes poor humidity control.

When performing a refrigeration load calculation, what does the 'sensible heat ratio' (SHR) indicate?

Answer: The proportion of the total cooling load that is sensible (temperature-changing) versus latent (moisture-removing)

SHR describes what fraction of the total cooling load involves lowering air temperature (sensible) versus removing moisture (latent), which affects evaporator and system selection.

In a refrigerated display case load calculation, what is the 'radiation load' component?

Answer: Heat transferred from warm surrounding objects and customers via infrared radiation to the open case

Open refrigerated display cases receive significant radiant heat from store lighting, warm customer bodies, and surrounding warm surfaces, which must be included in the load calculation.

What impact does increasing the evaporator TD (temperature difference) have on relative humidity inside a refrigerated space?

Answer: It decreases relative humidity because the colder coil aggressively removes moisture from the air

A larger TD means the evaporator surface is much colder than the room air, causing aggressive moisture removal and lower relative humidity, which can dry out stored products.

When sizing refrigeration equipment, what is the purpose of accounting for 'motor heat' from evaporator fan motors?

Answer: To include the heat added to the refrigerated space by fan motor electrical energy converted to heat

All electrical energy consumed by fan motors inside the refrigerated space is ultimately converted to heat, adding to the refrigeration load the system must handle.

What is the primary reason for calculating a separate 'pull-down load' distinct from the steady-state storage load?

Answer: The system may need significantly more capacity during the initial temperature reduction than it does for steady-state maintenance

Pull-down loads (cooling a warm space to setpoint or pulling in large amounts of warm product) are often several times the steady-state load, and the system must be capable of handling this peak demand.