HI
I am trying to model a room with 80% glazing which has a wall unit air
conditioner.
what will be the difference PTAC using electric heat / heat pump for heating
?
which one is advisable in terms of efficiency and energy savings?
does anyone has any thought on this?
Thanks
Regards
Deepika
PTAC and PTHP
Nov 4, 2010
A heat pump are a MUCH more efficiency way of heating. The only issue with
heat pumps are that they do not work well in cold weather (<40*F) below this
temperature, they are pretty much electric resistance heaters. A lot of
improvements have been made, for example, the Mitsubishi Citi
Multi-Split systems can operate at temperatures as low as 13*F. For these types
of systems, they operate as Heat pumps at 40*F and above. At 40*F and below,
they use electric resistance heat to warm the air flowing over the outdoor unit
(allowing for heat transfer between the air and the refrigerant). So once you
get down to 13*F they start to use a lot of electric resistance heating. Still
much better that pure electric resistance heating!
-Eddie
In addition to Eddie's comments, I would advise referring to
manufacturer's documentation for heat pump performance. Performance
varies by brand, model, capacity, and ambient conditions. I have
experience with several heat pumps operating well into the teens. Others
claim they can perform well below zero. Capacity charts and performance
curves will tell you what the capacity is at various conditions. For the
purposes of your model, I would ensure that you are using performance
curves reflective of the equipment you intend to install in your room.
Gary Schrade
Oops, I meant to say -13*F in my previous post (in reference to the Mitsubishi
Citi Multi-Split operating temperature)
thanks for the suggestions..
For my model, I am trying to figure out which unit will give me maximum
energy savings and which can also be used in real life project. I want to
validate the modeling results with actual performance results. and then
decide which equipment will I actually install in my room.
Thanks
Regards
Deepika
Eddie:
I never heard of a heat-pump that uses a electric resistance heater to warm the
air over the outdoor coil. I am working on a Citi-Multi project now and looked
up the wiring diagrams in their 676 page engineering manual. They do not
indicate an outdoor auxiliary heater besides the crankcase heater for the
compressor.
Some heat pumps have an auxiliary heater for the indoor units to warm the air
when the heat pump is in reverse mode for outdoor coil defrost and as
supplemental heat.
The Citi-Multi has a COP of 2.4 at 17 degrees F, which of course is 2.4 times
more efficient than electric resistance heat.
Paul Diglio