Throttling Range and Pipe Insulation

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Good morning eQUEST users,

I have two requests:

1) What is the definition of "throttling range"? I have always
had 0 until my last project which is a Police Station. We do mostly
energy retrofits and the existing boiler, 37 years old, has an input of
450 MBH. The total HVAC load is 222.651 MBH per eQUEST. For the first
time Report BEPU shows my base case model to be 34.1% outside of the
throttling range. What does this mean? The % of hours any plant load
is not satisfied is 0.

2) I have a church to model, starting this morning, which has no
insulation on the steam piping and we want to determine the savings by
putting 1" of fiberglass on the pipes. Usually we would
determine the savings in e-plus but is there any way to model this in
eQUEST? There are other measures and it would be convenient to have
everything in one report.

Walt Henry

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Look at the Detailed Simulation Reports Summary PDF documents (should be
in your eQUEST install folder) - it explains the difference between the
two.

Vikram Sami, LEED AP

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Throttling range is defined as the number of degrees F the zone
temperature needs to be away from setpoint for the VAV box to be fully
open or the heating or cooling coil valve to be fully opened. So, if you
have a VAV system and are setting the throttling range to 0, those boxes
are going to be modelled as fully opened whenever the space is not
completely satisfied. (Rereading your message -- that is probably not
what you meant by 0). Depending on your system -- 2 to 4 degrees F is
probably reasonable.

The BEPS is telling you that there are hours outside the throttling range
(underheated or undercooled hours -- see SS-R report or air side summary
for all systems in eQUEST interface to find which zones have problems;
SS-O helps tell when underheated/undercooled hours are happening) but that
plant has sufficient capacity in all hours.

In the heating circulation loop, there is a tab for "losses" where you can
put in a UA value for the uninsulated piping as well as defining where
that heat loss goes. You can then decrease the UA in a parametric run to
model the pipe insulation. Have not done this too much though but in
theory...

bfountain's picture
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The definition of throttling range is not completely correct. Throttling
range is the temperature band between no output and full output, with the
setpoint in the middle of the range. If the VAV cooling setpoint is 76F
with a throttling range of 2F, then the VAV box is at minimum position at
75F, and at maximum at 77F.

The BEPS and BEPU reports count hours as outside the throttling range if the
zone temperature is more than 1F outside the temperature band. In the above
example, a zone greater than 78F or less than 74F would be considered out of
control.

Steve Gates

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Walt,

1) This means that you have a zone that's not getting heating or
cooling when it wants it. 34.1% probably means there's an issue with
your system topology or your system really has unmet load hours in real
life. If you have one thermostat and lots of rooms with different
internal loads and exposures you're guaranteed to get a lot of unmet
load hours. The plant having zero unmet load hours means the plant is
satisfying all the requests its getting from equipment that serves
zones. So the zones aren't getting what they want from AHUs, radiators,
etc. but the plant is doing everything AHUs, radiators etc. want it to.

2) Any piping downstream of a steam control valve in a two-pipe
system in the same space served by the radiator doesn't need insulation
because it's acting as a radiator. In a one-pipe system,0 if you have
TRVs on the air vents, any pipe that only serves one radiator and is in
the same space as that radiator need not be insulated since it serves as
a radiator. If you don't have TRVs on your air vents in a one pipe
system (or in place of the control valves on two-pipe for that matter)
the insulation probably doesn't matter that much since all the radiators
deliver heat (and too much of it at that) at the same time as all the
uninsulated pipe. For the remaining pipe you'd estimate the surface
area of the piping to be insulated and multiply the U factor of the
insulation by the surface area of the pipe. Put that into the hot water
loop you're using as an analog for your steam system in detailed mode.

Daniel Bersohn, LEED AP

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Hello Daniel,

Thanks for your responses to my requests.

1) I did find the zone that was under heated in the reports. This
building has three zones and the basement was the under heated zone. I
changed the footprint to one zone per floor in lieu of perimeter/core
and dropped the percentage from 34.1 to 0.9 so I am content with that
since this is an existing system the we can't change.

2) I found the location of the losses tab in the water loop and see how
the UA can be changed so that should solve the pipe insulation savings
dilemma. I can't fully agree with you regarding the need to insulate
steam piping. Although the pipe does heat the zone it is in the process
of condensation in the piping degrades the quality of the steam reaching
the distributors, radiators in this case. This is a church and the
piping to be insulated is basically 400' of 4", 120' of 2" and 100' of
1". The function of the piping is to deliver good quality steam to the
radiators and without insulation on long runs, even if they are in a
heated zone takes away steam quality from the zone above and the
radiators in the zone where the pipe is located.

Thanks again!

Walt

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Hello walt,

Could you tell how did you change the footprint to one zone per floor or
send me a picture showing it? My model is also outside of the throttling
range and I'm trying to change it. I don't find where the option is.

Thanks a lot

________________________________

De: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] En nombre de Walt
Henry
Enviado el: martes, 26 de enero de 2010 22:19
Para: Daniel Bersohn; equest-users at lists.onebuilding.org
Asunto: Re: [Equest-users] Throttling Range and Pipe Insulation

Hello Daniel,

Thanks for your responses to my requests.

1) I did find the zone that was under heated in the reports. This
building has three zones and the basement was the under heated zone. I
changed the footprint to one zone per floor in lieu of perimeter/core
and dropped the percentage from 34.1 to 0.9 so I am content with that
since this is an existing system the we can't change.

2) I found the location of the losses tab in the water loop and see how
the UA can be changed so that should solve the pipe insulation savings
dilemma. I can't fully agree with you regarding the need to insulate
steam piping. Although the pipe does heat the zone it is in the process
of condensation in the piping degrades the quality of the steam reaching
the distributors, radiators in this case. This is a church and the
piping to be insulated is basically 400' of 4", 120' of 2" and 100' of
1". The function of the piping is to deliver good quality steam to the
radiators and without insulation on long runs, even if they are in a
heated zone takes away steam quality from the zone above and the
radiators in the zone where the pipe is located.

Thanks again!

Walt

Daniel Vilavedra's picture
Joined: 2011-09-30
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Hello Daniel,

In either Wizard the footprint screen has the choice for zones to be one
per floor or perimeter/core. See attached screens.

Walt

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Thanks a lot

Daniel

________________________________

De: Walt Henry [mailto:WHenry at thielsch.com]
Enviado el: mi?rcoles, 27 de enero de 2010 21:05
Para: Daniel Vilavedra; equest-users at lists.onebuilding.org
CC: JMcCarthy at thielsch.com; Jean-Paul Vandeputte; Marion McCarthy - Rise Engineering; NPrice at thielsch.com; Noel Chambers; Stephen Szewczyk
Asunto: RE: [Equest-users] Throttling Range and Pipe Insulation

Hello Daniel,

In either Wizard the footprint screen has the choice for zones to be one per floor or perimeter/core. See attached screens.

Walt

Daniel Vilavedra's picture
Joined: 2011-09-30
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Hello, Walt:

Do you think it can be changed in the Detailed Model? I checked about the Detailed model, it seems there's no functions to change footprint from one zone per floor to perimeter/core. .
Since you know, if we change the Detailed Model into Wizard Model, all the settings in the Detailed Model will be disappeared. That will be a great work load, I try that and found the only way is to copy all the settings from the old .inp document.

Eleanor Shen

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All,

Use care with zone simplification. The recommendation I made to use one zone per floor was because the system described usually doesn't have much effective zone by zone control in real life (especially true with one pipe steam), and in most instances looks something like one zone per floor. The solutions to the unmet load hours problem in these kinds of cases are to:

1) model one zone per physical room or thermal block and use your real life control zone and just live with the unmet load hours, but be careful as the model may do things that are unrealistic on the energy side in this case

2) model one zone per control in real life (i.e. if you have 3 thermostats, then model three zones) this may be more accurate in terms of energy for some cases, but may underestimate the real life unmet load hours of a poorly conditioned room within your real world system

If you have unmet load hours in, for example, a dormitory with a fan coil in each room, something's probably wrong with a schedule, an equipment capacity, or improperly defined system topology (system per zone, shell, site). Improper use of zone simplification techniques is bound to screw up your energy story. You'll end up getting results that don't make sense and you'll give your clients bad advice.

-Daniel

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