Product Pull-Down Time
Hours to pull product down from the refrigeration capacity dedicated to product load (hours = Q / capacity).
Example
You enter
- Product mass (lb) 2000
- Specific heat above freezing (Btu/lb-F) 0.9
- Entering temperature (°F) 80
- Storage (target) temperature (°F) 35
- Refrigeration capacity for product (Btu/hr) 3375
You get
- Pull-down time 24 hr
- Total heat to remove 81000
Checked against published worked examples from: Heatcraft Refrigeration Products.
Details, formula, and sources
ScopeThe inverse of Product Pull-Down Load. The note gives the usual design window (commonly 24 h) to compare the hours against.
Formula or tablehours = Q / capacity_btuh, with Q from the product pull-down relation (above freezing Q = m cp (t_enter - t_storage); freezing Q = m cp_above (t_enter - t_freeze) + m hif + m cp_below (t_freeze - t_storage); product entering at or below its freezing point: Q = m cp_below (t_enter - t_storage), no latent term). The inverse of product-pull-down-load (which returns rate = Q / hours).
Source and editionThe product pull-down time from the sensible-plus-latent cooling load and the available capacity, from ASHRAE Refrigeration, by name.
Free accessThe sensible-plus-latent product-cooling load is standard published refrigeration practice; the property tables are in the ASHRAE Handbook - Refrigeration.
What governsEstimate. AHJ and licensed professional govern.
API field namesmass_lb, cp_above, t_enter_f, t_storage_f, capacity_btuh, hours, q_btu
- Time hours = Q / capacity, the inverse of rate = Q / hoursalgebra
- Heat Q same sensible + latent product load as product-pull-down-loadASHRAE Refrigeration
- Property tables specific heats, freezing points, and latent heats from ASHRAEscope of this tile