[Equest-users] Simultaneous Heating/Cooling

[David Reddy]

If the chiller you are using is the "well-water-to-water HP" type
(CHILLER:HEAT-PUMP), I have successfully been able to  run a simulation with
this chiller connected to a CHW loop.  However, it was only connected to a
loop with a process chilled water load, and not connected to coils.

 

The loop-to-loop HP (CHILLER:LOOP-TO-LOOP-HP), which I believe Karen is
referring to, is intended to be attached to both a HW and CHW circulation
loops.  As I understand the DOE-2 help, there is an important difference
between these chillers in that the LOOP-TO-LOOP-HP chiller allows for
exchange of heat between the HW and CHW circulation loops, where as the
HEAT-PUMP chiller only moves heat to-and-from the CW loop (LAKE/WELL type).
You can connect multiple HEAT-PUMP or LOOP-TO-LOOP chillers to a single
LAKE/WELL loop and heat exchanger, so you could potentially have one chiller
supply your HW and one chiller supply CHW by adjusting the controls of the
2-PIPE loop.  Having them connected to the same CW loop, the total CW load
should be equal to the sum of the energy pulled out by the chiller in
heating, the energy put in by the chiller in cooling, and the loop pump heat
(plus loop thermal losses if simulated).  However, this is somewhat
irrelevant because no matter what the CW loop return temperature is, the
LAKE/WELL loop and heat exchanger will always provide the scheduled supply
temperature (or by default, the hourly ground temperature in the weather
file).

 

To get around this, we have developed an approach that takes the building
loads from the LAKE/WELL loop and applies them to a DOE-2 well-field model,
and in turn, takes the resulting well-field temperatures for use in the
building hourly simulation.  It requires post-processing and some iteration,
but I think this type of approach could be as good as we can do with the
existing tool.

 

Any other approaches out there?

 

David Reddy

Madison Engineering, PS

444 NE Ravenna Blvd, Suite 406

Seattle, WA 98115

 

 

From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Karen
Walkerman
Sent: Wednesday, February 04, 2009 8:58 AM
To: Tim Dion
Cc: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Simultaneous Heating/Cooling

 

Why are you using a separate lake/well loop and heat pump for the chilled
water loop?  You should be able to have the same piece of machinery attached
to both a chilled water loop and a hot water loop.  This way heat is
transferred from one loop to the other when there are simultaneous loads.
The ground loop is only used when there is net heating or cooling needed.

My beef with this system is that you can only use a loop type of lake/well
using a constant condenser water temperature.  This is usually not the case
with ground loops, unless you are circulating water from an underground
reservoir!

--
Karen



On Wed, Feb 4, 2009 at 11:38 AM, Tim Dion <TimD at hargis.biz> wrote:

I'm modeling a ground loop heat exchanger to provide condenser water to a
large water-to-water heat pump which will be capable of providing
simultaneous heating and chilled water to AHU coils in the building. The
Water-to-water Heat Pump being designed around is similar to that
manufactured by Multistack, Heat-Harvester, Climacool, etc.

 

I've successfully created a 2-pipe water loop with a water-to-water heat
pump that gets its' condenser water from a ground loop heat exchanger
(lake/well). When assigned to Fan Coils in the building this system appears
to work just fine. However, no simultaneous heating/cooling capability.

 

So, I've now added a chilled water loop with a second water-to-water heat
pump that gets its' condenser water from a seperate ground loop heat
exchanger. I then assigned the cooling coils to the chilled water loop and
the heating coils to the 2-pipe water loop. Trouble is I get the error that
reads, "the chilled water loop has no load". If I manage to get this error
to go away then my zones have 5,000 + hours of unmet heating loads. 

 

I've been searching the archives and I see that this has come up several
times but with no real solution other than "it should be able to be done".
I'm posting the question again in hopes that someone who has successfully
modeled this system can point the rest of us in the right direction. This
type of system is coming up more and more (I have 4 projects considering
them now) and as we strive toward greater building efficiency we are going
to HAVE to be able to successfully model these system types. 

 

Tim Dion, LEEDR AP 
Mechanical
HARGIS ENGINEERS 
600 Stewart Street 
Suite 1000 
Seattle, WA 98101 
 <http://www.hargis.biz/> www.hargis.biz 

d | 206.859.5391 
o | 206.448.3376 
 f | 206.448.4450 

 


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