[Equest-users] HVAC Capacity Increasing Consumption

Dakota Kelley dakotak at teliospc.com
Sun Aug 31 20:17:35 PDT 2008

Dear eQUEST Community,


I am a relatively new user transitioning from the wizard to the detailed
interface, and I'm having an issue with equipment capacity driving up
energy consumption.  In short, when I specify equipment capacities
(boilers and heat pumps) rather than let eQUEST auto-size, annual
electric and/or gas consumption increases by a factor of 10 or more.  I
feel I am misunderstanding how eQUEST views my system and am hoping
someone can point me in the right direction.  My .pd2 and .inp files are
attached for reference, and here's a quick description:


*         The building is a 280,000 SF multi-family high rise, and each
residential unit is served by a water-source heat pump.  There are nine
different sizes of heat pumps all served by the same building loop.  In
cooling mode, the building loop is served by an open cooling tower
connected via a heat exchanger.  In heating mode, the building loop is
served by two gas boilers.  The boiler loop connects directly into the
building loop without the heat exchanger.


*         In the DD wizard, I set up nine separate HVAC systems
corresponding to each of the different heat pumps.  They are all of the
"system per zone" type.  The differences between them are the
heating/cooling capacities, COP/EER, fan power, static pressure, and
CFM.  I entered everything but the capacities and CFM in the wizard, and
then I assigned each residential unit (which is synonymous with "zone"
in this case) to its corresponding system.


*         In the detailed interface, I inspected the system properties
for random zones/units under the Air-Side HVAC tab.  I found, for
example, that a unit served by a 26,200 Btu/h heat pump (cooling mode)
showed a total cooling capacity of only 433 Btu/h.  Another unit served
by a 56,200 Btu/h heat pump showed a cooling capacity of only 309 Btu/h.
I also noticed other small changes from the wizard, such as fan power
changing from 0.60 in WG to 0.52 in WG.  The fields for sensible cooling
capacity and total heating capacity were blank in the detailed
interface, as I would expect if they had been auto-sized in the wizard.


*         To see what would happen, I went through one floor's zones
(26,500 SF, 9.5% of the total) in the detailed interface and re-entered
the fan power, specified the heating/cooling capacities and zone CFMs.
After re-running the simulation, the annual consumption report showed
that space cooling and heat rejection (the cooling tower) both increased
by 100%, space heating increased by 32% and 41% on the electric and gas
sides, respectively, and pump power increased by 68.2%.  These increases
are for the whole building, not just the floor I modified.  If this
trend were to continue as I repeat for the remaining floors, total
consumption would obviously suffer tremendously.


So, my fundamental questions are:


*         Is the following a correct statement: specifying "system per
zone" in the wizard for a given size of heat pump, created as described
above, will cause eQUEST to replicate that system and assign an instance
of it to each corresponding zone within the detailed interface.  [The
low cooling capacities found in the detailed interface suggest they
might be summing to a larger total]   

*         Why are some values entered in the wizard not maintained in
the detailed interface? (i.e. the comment regarding fan power in bullet

*         Knowing that the equipment is not undersized, why does
specifying capacity drive up consumption so much?

*         Does the description above imply any other misconceptions?


Any insight would be extremely appreciated.  Thank you,


  Dakota Kelley

     Energy Analyst




3535 Travis Street, Suite 115, Dallas, TX 75204 | Phone 214.280.3825 |
Fax 214.744.0770 |  http://www.teliospc.com <http://www.teliospc.com/>
| dakotak at teliospc.com <mailto:mmcpike at teliospc.com> 


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