[Equest-users] PTAC and PTHP Outdoor Air Heater?

[Paul Diglio]

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




________________________________
From: Eddie Corwin <ecorwin at altanova-energy.com>
To: deepika khowal <deepika.khowal at gmail.com>; 
equest-users at lists.onebuilding.org
Sent: Thu, November 4, 2010 3:16:51 PM
Subject: Re: [Equest-users] PTAC and PTHP


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



________________________________
From: deepika khowal <deepika.khowal at gmail.com>
To: equest-users at lists.onebuilding.org
Sent: Thu, November 4, 2010 2:52:38 PM
Subject: [Equest-users] PTAC and PTHP


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
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