Condenser TD and Condensing Temperature (Dry or Wet Bulb)

The condensing temperature a condenser holds at a given ambient and design TD, and what moving that TD is worth in compressor power. The basis is the part that is most often got wrong: an air-cooled condenser's TD is measured from the DRY bulb, an evaporative condenser's from the WET bulb, and in most US summers the wet bulb runs well below the dry bulb -- so an evaporative unit at a wider TD can still condense cooler than an air-cooled unit at a tighter one. Reading a TD against the wrong basis produces a diagnosis off by the entire wet-bulb depression, which is why the basis is selected here and the answer names it. The leverage follows from a linearity and a sensitivity that are not the same thing: condenser capacity is roughly linear in TD, but compressor power responds to condensing TEMPERATURE, at very roughly 1.5 to 2 percent per degF over the ordinary range. So adding condenser surface until the TD drops a few degrees cuts compressor power by that much continuously, for the life of the plant -- which is why a dirty or undersized condenser is expensive rather than merely annoying, and why floating head pressure, letting condensing follow ambient down instead of holding it high, is the standard energy retrofit. The power sensitivity is ENTERED because it depends on the refrigerant, the suction condition, and the compressor; the default is a mid-range screening value. This does not size the condenser, compute the heat of rejection, look up saturation pressure, or establish the minimum head pressure the expansion valve needs. The condenser manufacturer's rated capacity at the design condition and the compressor's own performance data govern.

condensing temperature = ambient on the correct basis + TD; the change between two cases is that difference, and the compressor power change is that difference times the entered percent per degF; annual energy = compressor kW x that percent x hours, at 0.745699872 kW/hp.

Condensing temperature = ambient + TD as condenser practice writes it, with the basis distinction ASHRAE Refrigeration states: air-cooled TD from the DRY bulb, evaporative TD from the WET bulb. The compressor power sensitivity is ENTERED (commonly one and a half to two percent per degF) because it depends on refrigerant, suction condition and machine. It does not size the condenser, compute the heat of rejection, or look up saturation pressure.

One sum, one difference, and one entered sensitivity.

Estimate. AHJ and licensed professional govern.

Field names used by the API: condenser_type, ambient_f, design_td_f, alternate_ambient_f, alternate_td_f, power_pct_per_deg_f, compressor_hp, annual_hours, energy_rate_per_kwh, condensing_f, alternate_condensing_f, condensing_change_f, power_change_pct

• The basis is selected, not inferred air-cooled from dry bulb, evaporative from wet bulbASHRAE Refrigeration
• The power sensitivity is entered it depends on refrigerant, suction condition and compressorthe compressor's own performance data
• It does not size the condenser the manufacturer's rated capacity at the design condition governsthe condenser manufacturer