I'm comparing two systems one is a 4-pipe fan coil system and one is a
PTHP system. All of the savings between the two runs seem to make sense
except for a large difference in fan energy between the two. I don't have
detailed product information on the actual fan energy so I currently have
the same kW/CFM value input for both systems. The fan energy of the fan
coil system is 85% less than the PTHP system.
I believe the problem lies with the fan coil system, because it doesn't
have an option available for "Fan Control". I have the Indoor Fan Mode
set to Intermittent, which is how I believe the system would actually
operate since ventilation air is being delivered from a whole house fan.
Can anyone explain to me how the FC system calculates fan power? Why is
there no ability to change the fan control option?
Robby Oylear, LEEDR AP
Robby,
The PTHP system not only has a fan that recirculates inside air across the inside coil (evaporator coil when cooling, condenser coil when heating), but it also has a fan to blow outside air across the outside coil (condenser when cooling, evaporator when heating). The fan coil has only the inside fan. Perhaps the program is accounting for the energy for the outside coil fan, which might explain the 15% additional fan energy.
Keith Swartz, P.E., LEED AP
I don't think that's it. The PTHP system uses 600% more fan energy than
the fan coil system. It's 205,000 kWh for the PTHP system and only 28,980
kWh for the FC system.
Robby Oylear, LEEDR AP