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

DenmarkA/S Dantherm Jegstrupvej 4DK-7800 Skive

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

NorwayA/S DanthermLøkkeåsveien 26N-3135 Torød

Tel: +47 33 38 58 00Fax: +47 33 38 51 91

SwedenAB DanthermKabelgatan 12S-43422 Kungsbacka 1

Tel: +46 (0)300 16620Fax: +46 (0)300 16216

Dealer networkthroughout Europe.

08/97