If you have defined a single pump for the hot water loop,
then the pump affects the boiler AND the rest of the loop. If you have a
primary-secondary loop, then the primary pump affects (mostly) the supply side
(boiler) and the secondary pump affects the demand loop.
The Building Performance Team
James V. Dirkes II, P.E., LEED AP
1631 Acacia Drive NW
Grand Rapids, MI 49504
616 450 8653
From: EnergyPlus_Support@xxxxxxxxxxxxxxx
[mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of avdbree
Sent: Monday, August 30, 2010 4:47 AM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] Re: Manually sizing baseboards and plant
loops
An object Pump:ConstantSpeed (Flow Rate: autosize) is used
for the HW
loop. The object Boiler:HotWater has a variable flow mode. I am not sure
if this variable flow inflicts the HW loop or is just an internal aspect
of the boiler.
The model is run in E+ v.4.0.0.024.
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx,
Richard Raustad
<RRaustad@...> wrote:
>
> Are you using a variable-speed or constant-speed pump?
>
> avdbree wrote:
> >
> > I am investigating an existing building. The idea is to add
insulation
> > and keep the existing baseboards. So, the (new) heating can work
with
> > a lower supply temperature.
> >
> > When I autosize maximum (water) flow rates and/or UA-factors in the
> > objects ZoneHVAC:Baseboard:Convective:Water, Boiler:HotWater and
> > PlantLoop, I get a Delta T of the HW-loop up to 15 °K (which is
fine).
> >
> > Then I set myself maximum water flow rates for the baseboards (based
> > on the maximum heating rates from a simulation), while keeping the
> > flows of Boiler:HotWater and PlantLoop autosized. Delta T of the
> > HW-loop dropped to about 3 °K (which is to small). The results
for the
> > Zone Mean Air Temperatures and Baseboard Heating Rates are still
fine
> > (and similar to the autosized situation). Apparently, the flow in
the
> > HW-loop is quite big now and most of the flow during most of the
time
> > is going through the bypass on the demand-side of the HW-loop. This
> > increases the return temperature and decreases Delta T. A small
Delta
> > T is not economic.
> >
> > The occuring maximum loop flow in the HW-loop is exactly the sum of
> > all maximum water flows of all the baseboards (as specified in the
> > object ZoneHVAC:Baseboard:Convective:Water). So, I tried to set
myself
> > a lower Maximum Loop Flow Rate of the Plant:Loop (in order to lower
> > the bypassed flow and thus increasing Delta T). I choose the maximum
> > sum of all the baseboards water flows AT ANY GIVEN MOMENT. This
> > maximum is -- in my case-- less then half of the sum of all
> > (non-simultaneously) maximum water flows. And, by the way, about
twice
> > as much as for the completely autosized situation.
> >
> > But even when I manually set the Maximum Loop Flow Rate of the
> > Plant:Loop, the occuring flow in the HW-loop is still the (much
> > higher) sum of all (non-simultaneously) maximum flows of all
baseboards.
> >
> > Did I forgot to change another object too or is this a bug?
> >
> > PS. I tried to attach the idf-file but could not find the way to do
this.
> >
> >
>
> --
> Richard A. Raustad
> Senior Research Engineer
> Florida Solar Energy Center
> University of Central Florida
> 1679 Clearlake Road
> Cocoa, FL 32922-5703
> Phone: (321) 638-1454
> Fax: (321) 638-1439 or 1010
> Visit our web site at: http://www.fsec.ucf.edu
>
> UCF - From Promise to Prominence: Celebrating 40 Years
>
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