Alex,

When you select "water-cooled DX", I think the software is assuming the
rooftop MUA unit is essentially another water source heat pump on the same
loop as the others inside the building. Some of the ground source heat pump
manufacturer's actually make rooftop MUA units designed be installed as
such. An email to Carrier HAP software assistance could confirm this.

When you select "air-cooled DX", it is assuming the heating and cooling
sources are totally separate so they don't limit the heating source options.

Hope this helps,
Aaron

Aaron Smith, P.Eng
M&R Engineering Ltd.

----------------------------------------------------------------------
Date: Wed, 4 Mar 2015 18:18:41 -0500
From: Alex Garofalo

Hi all,

I was wondering if anyone can shed some light on the primary systems that
HAP assumes when modeling "Equipment Type - Terminal Units" with "Air System
Type - Water source heat pumps" (using the Common Ventilation setup). The
part i find confusing is under the "Ventilation System Components" tab when
i activate the cooling and heating coils for my make-up air unit. The reason
i activate them is because in my cold climate I must minimally condition the
outdoor air before bringing it to the terminal unit. However, when i select
"Water-cooled DX" for the cooling coil, the only other choice i have for the
heating coil is "water source heat pump." If instead I select "air-cooled
DX" for the cooling coil, i have much more variety of systems for the
heating coil. For the cooling coil, i'm assuming water-cooled DX refers to a
split condenser unit that is water-cooled perhaps using a cooling tower(?),
but then i don't understand what they mean by water source heat pump for the
central heating coil. Can someone help me understand the system setup for
the heating and cooling coils when i select water-cooled DX?

Thanks