Transcript Ductless Heat Pumps - Northwest Building Efficiency Center

Ductless Heat Pumps
Sizing Example
www.nwBuildings.org/dhp.aspx
[email protected]
Gary Nordeen
Bill Kingrey, P.E.
11/5/08 AFE Webinar
Introduction
This presentation is intended to show
how a ductless heat pump is sized for
a particular space.
The example is a maternity room inside a
health facility, that needs supplemental
cooling.
Heat Loss Calculations
Calculate the heat loss through walls,
glass, ceiling/roof, floor and any other
building components in the zone to be
served, using ASHRAE procedures
(chapter 26, Fundamentals)
Heat Gain Calculations
• Survey each zone and estimate heat
gains from lights, equipment
(computers, copiers, etc), people,
building envelope and ventilation
• Calculate both sensible and latent
(water vapor) loads
• Use ASHRAE Handbook of
Fundamentals Chapter 26
Heat Gain Calculation
Example
Assume we are going to provide cooling
to a maternity room that is currently
heated and ventilated by a central
system with heating and ventilation air.
We surveyed the room and found the
following existing conditions.
Maternity Room Example
• 2 fluorescent lights at 32 watts each ballast heat included
• 2 People @ 275 BTUH sensible, 105
BTUH latent (water vapor)
• Equipment = 1 computer = 65W
• Vent. Air = 40 CFM outdoor air at
ambient temp in summer, 70 in winter
• Envelope (windows, walls and roof)
calculated gain = 4,800 BTU
Maternity Room Example
Sensible Cooling Loads
• Lights + Equipment + People =
2x32 + 65 + 2 x 275 = 679 watts
679w X 3.412 BTU / watt = 2317 BTUH Sensible
• 40 CFM Ventilation Air at 92dB, 74wB =
40CFM x 1.08 BTUH / CFM x ºF x (92ºF – 75ºF) =
734 BTUH
• Total Sensible Cooling Load =
4,800 BTUH (envelope) + 2,317BTUH + 734 BTUH
= 7,850 BTUH Sensible
Maternity Room Example
Calculate Latent Loads
To calculate latent loads, use a
Psychometric Chart or software that will
determine enthalpy and density of
water/air mixtures
Psychometric Chart
Psychometric Calculations
• Or you can use this free online
program that will calculate enthalphy,
density, relative humidity, etc.
http://www.gorhamschaffler.com/psy.htm
Latent Cooling Loads
Assumptions:
• Ventilation air is cooled and dehumidified
to 75°FDb (dry bulb) at 30%RH (relative
humidity)
• Cooling design conditions at the site were
86Db and 68 Wb (wet bulb)
Latent Cooling Loads
• People = 2 x 105 BTUH = 210 BTUH latent
• Ventilation Air = 40ft³/min at 86Db/68Wb
• 13.55 ft³ of air at that temp = 1 lb of air
• In one hour we will cool 40ft³/min x 60 min/hr/13.55
ft³/lb = 177lbs/hr of air
• Air at 86dB/68wB contains 32.21 BTU/lb (of air)
• Air at 75dB/30% RH = 24.05 BTU/lb
• It will require 32.21- 24.05 = 8.16 BTU for each pound
of air cooled
• Total Ventilation Load = 177 lbs/hr x 8.16 BTU/lb
= 1,440 BTU/hr
• Latent Load = People + Ventilation Air
= 210 + 1440 = 1,650 BTU/hr
(about 1.5 pints of water per hour)
Selecting Ductless Heat Pump
• Pick a unit that has a capacity greater
than or equal to the total cooling load
• Mini-splits express heating and
cooling capacity in kW. To convert to
BTUH multiply the kW rating by 3412
More Information
Northwest Building Efficiency Center
866-929-6232
[email protected]
www.nwBuildings.org