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setback
thermostats
are
not recommended on
radiant
floor
systems due
to
the response
time
of
the slab.
B. Baseboard Heating
Another
application
of
hydronic heating
is
finned
tube
baseboard
heating. This
is
the
same
tubing
used
with
boilers with
one
major
difference.
The discharge
temperature
of
a
boiler
is much higher than geothermal
heat
pumps.
The
heat
pump
system
should
be sized at
115oF
hydronic leaving water temperature to maintain
efflrciency.
At
a l25oF leaving water temperature,
the heat
pump is
at
a
maximum
operating temperature
and
may
start to
trip
offon
high
head
pressures. Standard 3/4"
finned
tube baseboard
conductors
have an average
output
of
230
Btuhfft
at
120T
hydronic leaving water
temperature. In
most
cases
there
is
not
enough
perimeter
area
in
the
conditioned
space
to
allow for
the
required
length
of
tubing to
handle
the entire heating
load.
There
have been successful
installations using
baseboard
heating
as
supplemental heating using
the
forced
air
side
of
the
GeoSource
DualTEK
unit to
satisfy
the
heating load.
Cast
iron
radiators have
also been used
successfully.
If
these
radiators
are
rated
for
an
output
of70
Btuh/square
inch
at
a
130oF
hydronic
leaving water temperature, they
work well with
geothermal systems.
Although
the
radiator
may be
rated
at
130'F,
the system
should
still
operate at the
standard
115"F
leaving water temperature
of
the
hydronic
side
of
the heat
pump.
C. Other
Applications
Additional
open
loop
hydronic
applications
such
as
outdoor swimming pools, hot tubs,
whirlpools,
tank
heating, etc.
are
easily
sized based on heat
exchanger
operating temperature
and
flow.
The worksheet
in
Appendix
I
was
taken
from
the
ASHRAE
95
Applications Manual
and can be used
for
outdoor
swimming pool
sizing.
In
many
instances,
sizing
a
heat
pump to
these
applications
comes
down to recovery time.
The larger
the heat
pump
(within
reason
to avoid short
cycling)
the
faster the
system
recovery time
will
be.
eNote:
Installing
a
plate
heat exchanger
(see
Figure
3
for
an
example) between
the heat
pump
and an open
system is
required when corrosive
fluid
is
used
in
the
open
loop,
especially on swimming pools
where
pH
imbalance
can damage the heat
pump.
eNote:
Expect
the
maximum operating temperature
of
an
indirect
coupled application to be l0oF below
the
maximum
operating temperature
of
the heat
pump.
Other
forms of
closed
loop
systems such
as
indoor
swimming
pools, pretreated fresh
air
systems,
snow
melt
systems, and
valance heating
systems are also
very
corrmon with
GeoSource
DualTEK
heat
pumps.
The
sizing
of
the heat
pump to
these systems
is more precise
and
information from
the
system
manufacturer is
required.
V.APPLICATIONS
OF
HYDRONIC SIDE HEAT
EXCHANGERS
This
section
deals
with
some
common practices
used
when
coupling
the
hydronic
side
of
an
ECONAR
GeoSource
DualTEK
heat
pump to
the space
conditioning
heat
exchanger. There
are
so
many possible
applications
for
these systems
that they cannot
all
be
covered
in
this
text.
Hopefully
these ideas can
help
in
many
of your
system designs.
cNote:
Actual
systems
must
be
constructed to
all
appropriate
codes and
according
to
accepted
plumbing
practices.
A.
Storage Tanks
Coupling
the
hydronic
side
of
the heat
pump
to
the
space
conditioning
heat exchanger
through
a
water
storage
tao_k
is very
common. In
fact,
the
only
instance where
these
storage
tanks
are
not recommended is when
the heat
pump
is
coupled
to
a
large
heat exchanger
capable
of
absorbing
the
entire heating capacity
of
the heat
pump
(see
Figure
2).
In
applications
rhat
use
multiple
smaller
zones, storage
tanks
absorb the
relatively
large amount
of
energy supplied by
the heat
pump,
in
order to provide
longer run times
and less
compressor
cycling for
the
heat
pump.
Storage
tanks
also serve
to
dispense
energy
in
small amounts
so
that
the
conditioned
zones have
time to
absorb heat
without requiring
high discharge water
temperatures. Insulated hot water
heaters are
commonly
used
for
storage tanks.
cNote:
While all
hot water tanks
are
insulated on
the
top
and sides,
many do not
have
insulation
on the
bottom.
An
insulated
pad beneath
uninsulated tanks
will
reduce
energy
loss to
the
floor.
When
properly
sized,
a
storage
tank eliminates many
problems
with multiple
zone
hydronic
systems.
These
problems include
excessive
leaving water temperature
if
a
single
zone
cannot dissipate
heat
quickly
enough and
hydronic
flow
reduction through
the heat
pump when
only
one zone
is
calling.
This may occur
because the
hydronic
side
circulating
pump is
normally
sized
to
provide
the
heat
pump's required
flow
with all
zones
calling.
When
sizing
storage
tanks to
the heat
pump,
a
good
rule
of
thumb
is ten
gallons
of
storage
tank per ton
of hydronic
capacity.
The tank temperature
can be
controlled with
a
simple
aquastat
or
a
setpoint
controller.
The setpoint
controller
senses
tank water temperature
and
outside air temperature
to
increase the
tank temperatwe
as
the
outside
air
temperature
goes
down.
This confrol
scheme
provides
the
highest heating efficiencies by
requiring
the
lowest
possible water temperature to
heat
the space. Setting
the
optimal
design temperatures
in
the
controller
is
difficult,
5
:
-)
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