[Bldg-sim] Snow melt (UNCLASSIFIED)

Nick Caton ncaton at smithboucher.com
Fri Jul 22 14:26:27 PDT 2011


I will say I got really excited this past year about the isolated idea
of combining snow melt with geothermal well field design...

For those unfamiliar, well fields in this part of the Midwest (KS/MO/NE)
historically heat up over the long haul, especially with intense
equipment loading like John's situation...  fields installed decades ago
commonly end up struggling and failing when the extreme summers roll
around, sooner or later. 

The most common pre-emptive/patch solution I've seen to tackle this
trend is to tack on (or set up infrastructure for) an exterior dry
cooler to reject excess heat from the loop. 

I pushed hard recently to consider a "snow melt" loop (even if not used
to functionally melt snow) as a better "free" means of keeping a
well-field in balance annually, but the real trick is in how to set it
up so that this extra loop it doesn't require active
maintenance/monitoring... Making a location for horizontal loops like
this is also a challenge in many cases where the land is not readily
available or has future expansions planned.  Most clients out there,
even those with motivated maintenance staffing, would really be best
served with a "fire and forget" system that could handle itself decades
down the road without requiring active monitoring/adjusting as the
seasons change and temps swing. Ultimately, I haven't yet come up with
any particularly great setup that I would consider fool-proof over the
span of decades, but I'd be very interested if others have
thoughts/details to share on how this might be achieved.

Conceivably, and to your specific questions John, I'd speculate the
actual controls would at a minimum need to define parameters
establishing a range of "target" loop temperatures for the cooling and
heating season (these would be based on 1st year loop simulations, to
start).  The "melt" loop routed near the surface (or embedded in
concrete where it might be safe), would be normally closed, but valves
would open for circulation when the outside temperatures* are conducive
to pushing the well field return temperatures in the desired direction.
Done cleverly, you could push the system to permit water below the
setpoint during the cooling season, and above the setpoint during the
heating season as well (this behavior would potentially occur in the
swing seasons - spring/fall).  I'm thinking the ideal controls would
constantly monitor and take advantage of free heat rejection & free heat
gains whenever applicable.

* Another point to consider:  What temperatures are ideal to monitor for
such a loop?  Outside air data may be easily available, but considering
the lag in topsoil temps and depending on what you choose for the actual
loop installation location you might do better to locate a sensor
elsewhere... A loop underneath black asphalt getting will experience
different temperatures than the same loop embedded in light-colored
hardscape or simply under exposed topsoil.

Northern climates might find the same setup of interest to primarily
gain free heat gain to keep loops in balance, routing the secondary loop
through building envelopes or similar massed structures that would pick
up extra heat in the summer months.

Suffice to say I find it an interesting topic - if anyone has ever come
across a design guide or white paper on this subject I'd also be very
interested to hear about it!

~Nick

NICK CATON, P.E.
SENIOR ENGINEER

Smith & Boucher Engineers
25501 west valley parkway, suite 200
olathe, ks 66061
direct 913.344.0036
fax 913.345.0617
www.smithboucher.com 


-----Original Message-----
From: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Eurek, John
S NWO
Sent: Friday, July 22, 2011 3:30 PM
To: bldg-sim at lists.onebuilding.org
Subject: [Bldg-sim] Snow melt (UNCLASSIFIED)

Classification: UNCLASSIFIED
Caveats: NONE

Modelers.

One of my projects has server rooms which combined produce 143 MBH (more
heat
than some home furnaces) and the servers run all the time.  
I am designing a ground source heat pump system for the building.  The
energy
model shows that the geothermal well field is unbalanced by 522,500,000
btu.
I'm plan on using a snow melt system to get rid of the extra heat. (Snow
melt
is a nice by product, the goal is to balance the well field's annual
load.)

Has anyone designed this kind of system?
I'm not really sure how to model it?
I'm foggy on how to control it so I get rid of just the right amount of
heat.
Has anyone designed this kind of system?

It is fun to get to design energy efficient systems and coming up with
new
ideas, but it is hard to do research on them.  (I know snow melt isn't
new,
geothermal isn't new, computer room cooling isn't new, but I haven't
found
any articles tying the three together.)



John Eurek PE, LEED AP
Mechanical Engineer,
US Army Corps of Engineers
Omaha District CENWO-ED-DA
1616 Capitol Avenue
Omaha, NE 68102
Phone: (402) 995-2134
email: john.s.eurek at usace.army.mil



Classification: UNCLASSIFIED
Caveats: NONE


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