Which appliance is known for having low limits?

The make-up air unit is known for having low limits, primarily because it functions to replenish indoor air that has been exhausted from a building. These units often operate with a focus on maintaining indoor air quality and ensuring adequate ventilation. They typically introduce conditioned outside air to replace the air that is expelled, and in doing so, are designed to work efficiently even with varying external conditions.

This focus on providing a steady supply of air with minimal energy expenditure leads to lower operational limits. For example, they may not need to reach the high temperatures or pressures seen in systems like boilers or refrigeration units, which are designed to handle more extreme conditions within their operations. In contrast, other appliances, like heat exchangers or boilers, are designed to operate at higher limits for efficiency and functionality, such as producing steam or heating water to significant temperatures.

This understanding of the operational parameters and intended function of make-up air units highlights why this appliance is associated with low limits, making it the correct answer in this context.