H E A T R E C O V E R Y
W I T H H E A T P U M P S &
D E H U M I D I F I E R S I N
S W I M M I N G P O O L S
T H E M O I S T U R E Q U E S T I O N
2
High relative humidity and condensation
in a swimming pool hall is a major
problem. The fabric of the building will be
damaged because water vapour will
condense on cold surfaces and cause
corrosion, decay or fungal attack.
Windows will become steamed up and the
pool hall environment will become
uncomfortable for the occupants.
Unfortunately a swimming pool gives the
ideal conditions for warm water to
evaporate into the air as water vapour. It
is impossible to eliminate water
evaporation altogether, but with a
carefully designed ventilation system the
evaporation rate can be minimised, and
together with a thermally insulated
building, the relative humidity of the pool
hall can be controlled to a safe and
comfortable level.
If room conditions of 28°C/65% RH are
required the dew point will be 21°C and if
the outdoor temperature is -10°C the
construction must have a very high
insulation value to prevent condensation.
Whilst maintaining a quality pool
environment it is equally important to
consider the financial implications of
achieving such conditions.
Ventilation with heat recovery,
dehumidification and correct control in
accordance with the various conditions in
a swimming pool hall are all factors which
are included in a Dantherm swimming
pool plant. The various possibilities are
discussed in more detail later in this
publication.
3
EXAMPLE
Swimming pool halls must be designed
and constructed to comply with a number
of demands, requirements and needs.
When considering the design of the
building, environmental demands must be
taken into consideration just as the
interests of the various groups of users
must be considered.
Today a swimming pool hall is not only for
the sportsman requiring competition
pools of international dimensions. There
must be room for general exercise
swimming, family fitness and fun,
relaxation and socialising.
During the design process, consideration
should be given to the following
requirements:
■ Competition use.
■ Leisure use.
■ Diving facilities.
■ Spa and therapy use.
■ Wave generation and other water
movement techniques such as chutes
and rapids.
No matter how the available space is
distributed and no matter how big the
space is, there are certain demands on the
internal climate, as mentioned on the
previous page.
The design engineer must provide a
solution which ensures that temperatures,
humidity and fresh air are correctly
controlled at all times and at the lowest
possible energy cost.
DanX ventilation plants from Dantherm
have all the features needed to comply
with all the above-mentioned demands
and provide an ideal solution.
These plants are specifically designed for
use in swimming pool halls. They are
flexible, resistant to aggressive
atmospheres and they provide energy-
saving ventilation and dehumidification,
and exact control of the parameters which
can be expected in swimming pool halls.
Swimming pool halls also incorporate
other areas, such as changing rooms,
bathrooms, cafeteria etc. The demands
on the interior climate in these areas are,
of course, all different and they will
typically be connected to separate
ventilation plants. Whatever the mix of
requirements may be, the DanX range
offers a perfect solution which can be
individually tailored to suit a particular
project.
D E S I G N P R O C E D U R E F O R S W I M M I N G P O O L S
4
A simple solution for swimming pools or
secondary rooms is the standard DanX unit.
A plate recuperator is built into all models
and can be considered as the core of the
unit, extracting up to 75% of normally
wasted heat from the exhaust air.
This efficient recuperator is made of
anodised and epoxy coated aluminium and
is resistant to the aggressive atmospheres in
swimming pool halls. To ensure an even
longer life these plants can be supplied with
internal surfaces treated with powder
enamel (Corrosion class 3).
DanX plants are available with two-speed
fan motors. With precise control via a
hygrostat, energy costs can be reduced by
operating the DanX at half speed for certain
periods. As an alternative to the two-speed
fan motors, the plants can be fitted with
single-speed motors which are controlled by
means of a frequency converter.
DanX WITH HEAT PUMP
For additional heat recovery the DanX plant
can be supplied with an air to air heat
pump. This version is available with one or
two compressors. The coefficient of
performance (COP) will be improved to more
than 4:5.
DanX plants incorporating a heat pump offer
the further advantage that they can cool
warm outside air being supplied to therapy
rooms in the summer.
As an extra facility the heat pump can be
fitted with a water-cooled condenser
allowing excess recovered heat to be
returned to the swimming pool water or the
building’s hot water system.
DanX WITH MIXING BOX
When the DanX plant is fitted with a mixing
box the fresh air supply can be reduced by
recirculating part of the pool hall air. It may
also be necessary to reduce the supply of
fresh air in cold periods to prevent the heat
VENTILATION & DEHUMIDIFICATION IN SWIMMING POOL HALLS
exchanger from freezing. Using a mixing box
thus offers several advantages.
DanX USED AS A DEHUMIDIFICATION PLANT
When the DanX plant is fitted with a mixing
box, the heat pump can be used as a
dehumidifier. An extra damper can be built
i n
in addition to the by-pass damper which is
shown on the drawing. When the plant is
working as a dehumidifier with recirculation
through the mixing box, the extra damper
will reduce the air volume passing across
the evaporator and thus increase the
dehumidification capacity even more.
DANTHERM DEHUMIDIFIER
Dantherm has a wide range of
dehumidifiers. As mentioned above, the
DanX plant incorporating a heat pump can
be used as a dehumidifier. The principle is
the same as smaller dehumidifiers which
recirculate air (such as those described on
pages 10 and 11), which are used in private
swimming pools. The principle is shown on
the drawing below. The air from the hall is
drawn in and passed through a dehumidifier.
It then passes over evaporator coils where
the air is cooled down to a temperature
below the dew point allowing water vapour
to condense into water droplets which are
collected in a drip tray. The air flow then
passes through a compressor and, if fitted,
a water-cooled condenser. Having passed
through a warm condenser coil and an after-
5
+ +
DanX without heat pump
Heat pump dehumidifier
DanX with heat pump
DanX with heat pump and mixing box
6
50
Amount of evaporation from pool (g/m2)
60 50 60 50 60
204 182 197 174 190 165
217 194 209 187 203 178
230 108 223 200 216 191
235 213 229 204
244 219
50
182
194
208
221
236
250
60
156
169
182
195
210
223
50
187
118
213
228
243
259
60
158
172
185
200
215
230
50
192
205
220
235
250
268
60
162
175
190
205
221
238
50
196
211
226
241
259
277
60
164
179
194
209
227
244
Air Temperature ˚C/Relative Humidity % RH24 25 26 27 28 29 30˚C
Water temp ˚C %RH
22
23
24
25
26
27
28
29
30
When choosing reasonable operating
conditions, moisture problems
as well as operational
expenditure can be
controlled. To minimise
evaporation rates the
pool hall temperature
should always be higher
than the pool water
temperature. The higher
the temperature differential
between air and water the lower the
evaporation rate from the pool surface.
However, in order to maintain a reasonable
operating economy, the difference should not
be bigger than 2-3°C.
In public swimming pools the pool hall air
temperature is usually 29/30°C with the water
temperature a degree or two below that.
Hydrotherapy pools usually have a water
temperature of 35-37°C.
VENTILATION WITH HEAT RECOVERY
The object of the ventilation plant is to
maintain the design temperature and humidity,
and to secure good air quality within the pool
hall. Air in a swimming pool hall will always
have a moisture content higher than that of
outside air. It follows therefore that by
introducing a calculated amount of fresh air
into the pool hall the desired relative humidity
can be maintained. This process has the
potential to use a great deal of energy so it is
essential to recover as much heat as possible
from the exhaust air, and to avoid changing air
more than is necessary. A DanX heat recovery
system complete with controls is the ideal
device for providing energy efficient, cost
effective control of the swimming pool hall
environment.
DESIGN PROCESS
The first step is to calculate the evaporation
rate, and then on the basis of this determine
the necessary maximum fresh air volume
required. These are then used to determine the
size of the DanX to be installed.
Evaporation from the pool surfaces and the
surrounding wet areas is the main contributor
to the moisture problem. The quantity of
evaporation depends on such factors as pool
area, water temperature, air temperature,
humidity, air velocity, and the bathing activity.
There are many formulae and rules of thumb
that profess to calculate evaporation rate. In
the examples below we have used the German
calculation formula VDI-2089 which states the
required data for the design of indoor
swimming pools. The calculations have been
converted to the tables shown below, including
quick-selection charts as well.
D E S I G N P R O C E D U R E F O R S W I M M I N G P O O L S
Necessary air changeThe fresh air volume, required to remove theevaporation can be calculated as follows:mL = mw
(xu – xi)mL = Mass flow, outside air (kg/s)mW = Mass flow, exhaust air (kg/s)xu = Moisture content, outside air (g/kg)xi = Moisture content, inside air (g/kg)The moisture content of the outside air (xu) variesaccording to the season of the year – from amaximum of 11 - 12 g/kg in the summer to 2 - 3g/kg in the winter.In practise xu should be set to no less than 9 g/kgwhich will only be exceeded for 15% of the yearand which is also recommended by VDI-2089.Besides condensation problems are rare in thesummer and the water content xi of the inside aircan therefore be a little higher.
7
The evaporation rate is calculated as follows:
W = ε x A x (PB – PL) (g/h)
A = Pool surface area (m2)
PB= Saturated vapour pressure at water temperature (hPa)
PL= Partial vapour pressure at air temperature/% RH (hPa)
ε = empirical factor g/(hhPa m2 h):
0,5 covered pool surfaces
5 calm surface
15 private swimming pool, not very occupied
20 public swimming pool, normal activity
28 leisure pool
35 wave pool
On basis of the formula and ε= 20 we have madethe diagram below to make the work easier.
Example: Public swimming pool.Pool size: 25 x 12m = 300 m2
Water temperature, 28°C (100%RH) PB = 37,8 hPaAir temperature, 30°C (60% RH) PL = 25,45 hPaMoisture Content, pool air xi = 14,9 g/kgMoisture Content, fresh air xu = 9,0 g/kgDensity of ambient air = 1.175 kg/m3
Evaporation W=20 x 300 x (37,8–25,45) = 74,1 kg/hrRequired Air Volume = 74,100 = 2,97 m3/s
(14,9–9) x 1,175 x 3600
Unit type will be a Dantherm type DanX 7/14.
C O R R E C T A I R D I S T R I B U T I O N
8
The air movement and especially the air
distribution of supply air into a swimming
pool hall is of great importance, of equal
importance to that of designing the
ventilation system with the correct air
volume.
Protection of the building fabric is the
primary objective of a swimming pool
ventilation system. The conditioned air
supplied to a pool hall is warm and dry
and does not condense as easily as
stagnant air, which has had time to cool
off. The incoming conditioned air should
ideally be supplied from low level around
the perimeter of the pool hall on three
sides and then extracted at higher level
on the fourth. It is important to
emphasise that all surfaces (especially
glazed areas) require an adequate supply
of air to prevent condensation from
forming.
On the other hand air movement above
the pool surface should be kept as low as
possible, as the air movement influences
evaporation. The more saturated the air is
immediately above the pool surface the
less water can evaporate.
Furthermore it is important that the
pressure in the pool hall should be
slightly lower than outside in order not to
press the vapour out into the fabric of the
D ATA
Model
9
3/6
5/10
7/14
9/18
12/24
16/32
1707
1707
1707
1920
1920
2650
XK
w
880
1400
1900
1800
2200
2200
d
1760
1760
1920
2350
2550
2800
h*
2270
2270
2270
2500
2600
3529
XWP
w
880
1400
1900
1800
2200
2200
d
1760
1760
1920
2350
2550
2800
h*
985
1200
1290
1550
1400
1500
VV & VF
w
880
1400
1900
1800
2200
2200
d
1760
1760
1920
2350
2550
2800
h*
880
1400
1900
1800
2200
2200
F
w
880
1400
1900
1800
2200
2200
d
916
475
475
600
600
700
h*
475
475
475
600
600
700
B
w
880
1400
1900
1800
2200
2200
d
1760
1760
1920
2350
2550
2800
h*
*Excludes base and adjustable feet 145–200mm common to all models
Dimensions in mm
The DanX exhaust air heat pump is a fresh
air ventilation system that recovers
normally wasted energy. It is a modular
system that uses a range of standard
options that allow a design to be as
simple or as sophisticated as is required.
All types are mounted in a strong frame
construction with insulated cover panels
made of galvanised plates. For use in
more aggressive environments, as for
instance in swimming pool halls, the DanX
plants can be supplied with powder
enamelled cover plates.
The core of the DanX features a cross flow
heat exchanger made of epoxy coated
aluminium capable of recovering up to
75% of energy from the exhaust air.
Further energy can be extracted using the
air to air heat pump system and in
addition to that a wide range of
accessories is available to cover the
various needs.
CONTROL
The control of the DanX unit is based on
a modern DDC control which makes it
possible to control all the functions of the
plant optimally. This kind of control offers
a variety of options and nevertheless it is
easy and simple to use thanks to the well-
10
DEHUMIDIFIER
TYPE CDP
Dantherm has a range
of small dehumidifiers
especially designed for
dehumidification of
smaller swimming
pool halls. The CDP
d e h u m i d i f i e r i s
designed to blend well
into the interior of private swimming
pools where its only purpose is to
dehumidify the room. The dehumidifier is
available in two sizes and it is easy to
install. Control is taken care of by a room
hygrostat.
Evaporation is calculated as described on
the previous pages. As the activity in a
private swimming pool is not as high as in
a public swimming pool, the evaporation
will be lower too, and this is allowed for
in the calculation formula. For this speci-
fic field it is easier to use a selection chart.
S M A L L S W I M M I N G P O O L S
and from the pool hall. The units can be
supplied with after heating coils which
will contribute to the
heating of the room.
Control is governed by
a thermostat and a
hygrostat.
CD dehumidifiers can
be supplied with water-
cooled condensers if a
temperature increase
from the air circulation
through the unit is not required.
As a further advantage the CD units
can be fitted
with ducts
allowing supply
o f
10-15% fresh air
with the inlet
air.
DEHUMIDIFIER TYPE CD
Type CD dehumidifiers are for bigger
swimming pools than the CDP types and
they are intended for plant room
installation which will reduce the noise
from the unit. The CD dehumidifiers can
be supplied with ducts carrying the air to
Condensate capacity at 30°C/80%RH Kg/24h
Working range, humidity %RH
Air volume m3/h
Height mm
Width mm
Depth mm
45
40-100
500
700
1008
270
74
40-100
750
700
1492
270
90
40-100
1500
650
1150
650
160
40-100
2500
835
1250
835
CDP20 CDP30 CD40 CD50
HEAD OFFICE
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Tel: +45 97 52 41 44Fax: +45 97 52 61 34
EUROPEAN CONTACTS
EnglandDantherm LimitedHither Green ClevedonNorth Somerset BS21 6XT
Tel: +44 (0)1275 876851Fax: +44 (0)1275 343086
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Tel: +47 33 38 58 00Fax: +47 33 38 51 91
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Tel: +46 (0)300 16620Fax: +46 (0)300 16216
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08/97