16:1 TURNDOWN FURNACES DELIVER PART LOAD COMFORT
Valent units offer high turndown furnaces, up to 16:1, enabling them to maintain comfortable discharge air temperatures at part load conditions. Why is this especially important with DOAS units?
DOAS and high outdoor air units can experience large entering air temperature swings. As heating demand and airflow vary, the need for a high turndown furnace increases, especially during times of low demand. If a furnace cannot turn down adequately, it will cycle on and off to maintain discharge air temperature set point, causing wide temperature fluctuations, space over-heating, and shortened furnace life.
WHEN IS HIGH TURNDOWN HEAT ESPECIALLY IMPORTANT?
To maintain comfortable space conditions, a high turndown furnace will be required when there is:
- Low demand
- No exhaust air energy recovery
- Heating capacity sized to provide backup for an energy recovery failure
- A supply fan that modulates from maximum to minimum speed
High turndown furnaces maintain comfort at part load conditions.
ACHIEVING HIGH TURNDOWN
Furnace turndown ratio compares maximum to minimum heat output. So, a 16:1 turndown furnace modulates from 100% to 6.25% (100 ÷ 16 = 6.25), and a 4:1 turndown furnace modulates from 100% to 25%. Below these minimum numbers furnace burners cycle or turn off.
Valent achieves a 16:1 turndown by utilizing both on-off and modulating gas valves to provide responsive control throughout varying heating demands and airflows.
