Okay, let's break down how to approach this HVAC unit's load calculation. Your drafters/engineers are right to be cautious and leaning toward conservative values.

Understanding the Ratings RLA (Rated Load Amps)

This is the expected current draw of the compressor motor under normal operating conditions. It's a good indicator of the typical load, but it's not the maximum the motor might draw.

FLA (Full Load Amps)

This is the current the compressor motor will draw when operating at its rated horsepower and voltage under full load. It's usually higher than the RLA. It's the value used for load calculations, unless you have information that clearly indicates a lower, more accurate value is appropriate and code-compliant.

Heater Package FLA

This is the current draw of the supplemental electric resistance heaters. It's a separate load from the compressor and must be added to the compressor load.

MCA (Minimum Circuit Amacity)

this represents the total maximum amount the equipment can draw at any one given time.

1. VA for Total Calculated Load

You need to consider all loads contributing to the total VA. Compressor

Use the compressor

FLA (Full Load Amps). As others pointed out, using the RLA is not conservative because the compressor can draw more than that. Heater Package

Use the

FLA (Full Load Amps) for the heater package. Other Loads

Include any other loads listed on the unit's nameplate, such as fan motors, controls, etc. Use their FLA or rated wattage/voltage to calculate the VA.

Formula

VA = (Voltage) x (Amps). For the compressor, VA_compressor = 240V x Compressor FLA. For the heater, VA_heater = 240V x Heater FLA. Then add those VAs together, plus any other loads.

Why Use FLA Instead of RLA? Safety Factor

The FLA provides a built-in safety factor. The compressor could draw this much current under certain conditions (high head pressure, starting, etc.). Designing for FLA ensures your wiring and overcurrent protection are adequate.

Code Compliance

Electrical codes (like the NEC in the US) generally require you to use FLA for motor load calculations, especially for continuous loads.

Overcurrent Protection

Overcurrent devices (circuit breakers or fuses) are sized based on the FLA to protect the wiring and equipment from overloads and short circuits.

2. Voltage for Calculation: 230V vs. 240V

Your drafters/engineers are being conservative, but here's the logic: Motor Rating

The compressor motor is rated for 230V.

Nominal Voltage

The nominal voltage of your system is 240V (single-phase). In reality, the voltage can fluctuate somewhat.

Conservative Approach

Using 230V results in a slightly higher current calculation (Amps = VA/Voltage). This is a more conservative approach because you're designing for a potentially higher current draw.

Code Considerations

The NEC (in the US) allows you to use the nominal system voltage (240V in your case) for calculations.

Recommendation


Use FLA for all the loads from the unit. This is code compliant and will ensure you design for the equipment's worst-case current draw.2. Use 240V for the calculation. It is not only the most accurate voltage to use in the real world, it is within the allowable variance that the motors can handle.

Important Considerations



Nameplate Data

ALWAYS rely on the actual nameplate data of the HVAC unit. Don't guess!

Local Codes

Be sure to consult your local electrical codes and regulations. They may have specific requirements for HVAC load calculations.

Continuous Load

HVAC equipment is often considered a continuous load (operates for 3 hours or more at a time). The NEC requires you to increase the calculated load by 25% for continuous loads when sizing conductors and overcurrent protection.

Voltage Drop

Check for voltage drop in the feeder conductors, especially if the run is long. Excessive voltage drop can damage the motor and other equipment.

In summary, use the FLA values for the compressor and heater package, and factor in other loads. While your drafters/engineers' caution about voltage is understandable, use 240V for your calculation.Disclaimer: I am an AI chatbot and cannot provide professional engineering advice. Consult with a qualified and licensed electrical engineer for your specific project.* Flag for review