[Equest-users] Question on a L2LHP with a Lake/Well GLHX

[Demba Ndiaye]

Do you mean the temperature of the fluid returning from the ground-loop heat exchanger?

I have relied on that at times, but it is not perfect. If someone knows a better way ....

______________
Demba NDIAYE

From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Otto Schwieterman
Sent: Monday, June 06, 2011 4:56 PM
To: TaylorRoberts at Eaton.com
Cc: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Question on a L2LHP with a Lake/Well GLHX

Taylor,

Make sure you specify the size for all of the water side equipment (Loop-to-Loop Heat Pumps, Boilers, and Pumps). If I let eQUEST size this equipment with a central geothermal system the default sizes are way off and the model does not give the results that you would expect.

You may want to consider using load management and equipment controls so the system operates in eQUEST as you want.

When you get close I would recommend creating a ground temperature schedule for the Ground Loop Heat Exchanger if the loop is a ground source loop. The Lake/Well loop gets the ground temperature from the weather file that is used (you have to select a lake/well loop for a central system). Has anyone created a ground loop temperature schedule? If you have, how did you determine the ground temperatures? My plan is to create the model as a geothermal heat pump system, get the ground temperatures from the hourly reports and create a schedule from the results. This is very time consuming but it is the most accurate way that I can think of to get the proper ground temperatures.

LAKE/WELL                 The loop return temperature is set equal to the temperature given by LOOP-TEMP-SCH, if specified. If LOOP-TEMP-SCH is not specified the monthly ground temperature from the weather file is used. This option allows you to simulate water-wells, lakes, and rivers, where the temperature of these sources is driven by factors other than the loop thermal demands. Since the supply temperature is fixed by the schedule, all keywords pertaining to the ground field definition are ignored.

                                  Note that a GROUND-LOOP-HX of TYPE = LAKE/WELL can be attached to CIRCULATION-LOOPs of  TYPE = WLHP, CW (condenser water), or LAKE/WELL. This allows chillers or other water-cooled components to be attached to heat sinks like a lake, well, or river rather than a cooling tower or outside air.
Good luck,

Otto

From: Paul Riemer [mailto:Paul.Riemer at dunhameng.com]
Sent: Monday, June 06, 2011 3:32 PM
To: 'TaylorRoberts at Eaton.com'
Cc: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Question on a L2LHP with a Lake/Well GLHX

Taylor,
Whenever anyone says VAV, I hear VAV with reheat so if you have reheat the following might help.

I believe the L2L heat pump assumes one refrigerant circuit, such that if it sees load on both loops it will have to meet both loop temperature set points regardless of the magnitude of either load.  So a lift of around 88 (= 130-42).  Do you want that and thus your boiler is truly back up?  You can end up with the tail wagging the dog where you punish the efficiency of the heat pump in cooling to meet a little reheat load.  Or would you rather have your boiler operating as a reheat boiler or in series with your condenser water heat exchanger?

I have worked more with the banks of water to water heat pumps that provide simultaneous heating and cooling by having some heat pumps in each mode, thus none working against the huge lift.  I end up modeling those as separate chilled water and heating water plants. No its not perfect but with the lake/well loop you were already going to be assuming a temperature profile and disconnecting your equipment from any model representation of lake/well capacity.

Those are very different approaches in design and in modeling, so I'd consider which you want.  Good luck.

Paul Riemer, PE, LEED AP
DUNHAM


From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Patrick Keeney
Sent: Monday, June 06, 2011 2:29 PM
To: Brian Fountain
Cc: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Question on a L2LHP with a Lake/Well GLHX

Thanks for your responses, Brian.

Where do you find these help files that you mentioned?  Are you talking about the tutorial and reference PDFs in eQUEST, or is there something more comprehensive like full project examples with the pd2 and inp files?






On Mon, Jun 6, 2011 at 3:02 PM, Brian Fountain <bfountain at greensim.com<mailto:bfountain at greensim.com>> wrote:
The added pumping power is likely from the default 200 ft of static pressure on the lake/well ground loop.  Try changing this.

I've only played with 1 of those system types but I found it was very sensitive to the 4 temperatures on the "Miscellaneous" tab of the chiller (and the defaults were not helpful -- but the values in the help file were.

Wish I could be of more help -- good luck.

Brian


On 6/6/2011 2:12 PM, TaylorRoberts at Eaton.com<mailto:TaylorRoberts at Eaton.com> wrote:
Hello everyone,

I am trying to model a HVAC system that is composed of a central geothermal system that uses a heater/chiller with back up boilers to provide hot and chilled water to AHU for a VAV air-side system. Following the advice I found on the archives from the Loop to Loop Heatpump in eQuest discussion I modeled a system with a L2LHP that uses a lake/well loop (see screen shot). I made sure to zero out the static head for the GLHX and changed the max hot water temp in the hot water loop to 130F to be compatible with a heatpump. I compared this system to a basic chiller/boiler VAV system to see if it showed any signs of improvement and the results have been very puzzling. The geothermal system is using slightly less energy to cool but isn't providing any heating to the system. Instead the boilers are providing all of the heating. When I remove the boilers to make the L2LHP provide all of the heating it is performing terribly using an enormous amount of electricity to heat. Also, I assumed that there would be a pumping power increase but the L2LHP is using about 3X the electricity as the boiler/chiller system and this seems way too large.

Has anyone had any luck modeling a system like this or has any ideas why my L2LHP model is using more energy than a standard chiller/boiler system?


Taylor Roberts, EIT
Energy Solutions Intern
Energy Solutions Group

E M C Engineers, Inc.
Eaton's Electrical Services & Systems
970-208-7917<tel:970-208-7917>
TaylorRoberts at Eaton.com<mailto:TaylorRoberts at Eaton.com>





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