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CYSENI 2011, May 26-27, Kaunas, Lithuania
ISSN 1822-7554, www.cyseni.com
1
EXTRACT AIR ENERGY UTILIZATION USING HEAT PUMP IN
BUILDINGS WITH INDOOR SWIMMING POOLS
A. Brahmanis, U. Pelīte, A. Lešinskis, D. Kona, T. Bui Kon
Riga Technical University
Kaļķu iela 1, LV-1658 – Latvia
Phone: +37129454525
Email: Arturs.Brahmanis@rtu.lv
ABSTRACT
An annual energy consumption simulation is made for one Latvian mansion with swimming pool hall.
Building has two main parts: living part (with bedrooms, living room, kitchen, and washing rooms),
and a recreation part with 28m² swimming pool, saunas and sports hall.
HVAC system consists of the following elements: heating system with convectors, water-to-water
heat pump system cooling / heating concrete slabs in living part, and centralized mechanical extract,
with natural outside air intake through the window grilles. Air –conditioning in swimming pool is
provided by separate air-handling unit with heat pump - dryer.
In winter the heat pump system heats concrete slabs, utilizing extract air energy through air to water
heat exchanger. In summer living room slabs are cooled, and removed heat is used for the swimming
pool supply-air preheating.
The annual energy consumption simulation is made with DOE 2.1E core based application, using
building’s information model (BIM) for the average Latvian meteorological year. Two BIM’s are
made: for a living part of the mansion and for swimming pool room, using design coefficients for
constructions’ thermal resistance and indoor air parameters.
Simulation results show, that swimming pool room consumes 77 MWh of heating energy per year.
When using heat pump gained energy to preheat swimming pool supply air, annual heat energy
consumption decreases to 62 MWh, which means about 20% saving. The heat pump system annual
average coefficient of performance (COP) according to manufacturer’s data is assumed as 2.5.
Paper results can be used by HVAC engineers and architects for ventilation and air conditioning
design in other multi-purpose buildings with indoor swimming pools.
Keywords: HVAC simulation, indoor swimming pool, heat pump.
1. INTRODUCTION
1.1. The brief of requirements for air exchange in Latvia
According building law rooms has to have balanced ventilation [ 1, 2]. For residential
buildings in Latvia is common using natural or mechanical extract. Mechanical extract in
many situations gives a possibility for heat recovery to supply air. However, in buildings
with decentralized natural supply air trough the windows, engineers have to find other ways
for heat recovery. The aim of this paper is to analyze the energy efficiency of extract air
energy utilization using heat pump in buildings with indoor swimming pools.
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1.2. Heat recovery with heat pump
Several types of air-to-air exchanger recovery devices are available for recovering
energy from ventilation. The heat exchanger may transfer sensible heat only or both sensible
and latent heat. Over many decades, plate type, regenerative wheels, and heat pipe exchangers
were developed and used to transfer heat for a variety of air-to air applications. Typical heat
and enthalpy exchange efficiencies range from 55 to 80% [ 3]. Heat pump energy recuperation
technologies are widely used and being researched for decades [ 4 , 5].
As a first step to make heat recovery is to place a heat exchanger in exhaust air flow.
Then heat recovery is possible for consumers with lower temperature:
• hot water preheating;
• snow melting on entrance road surfaces outside of the building (not considered
as advantage in building energy performance).
When using heat pump it is possible one more potential consumer – heating. Technical
data collected in table for building systems - hot water and heating is shown in Table 1:
Table 1. Heat recovery possibilities within the hot water and heating systems
Nr.
Recovery type
Hot water
Heating
1
Heat exchanger
Preheating ~ 7K.
Accumulation in buffer
tanks is hygienically and
technically not reasonable.
Not possible, when all rooms has
temperature higher then exhaust air
temperature. Limited possibility to
cover some part of heat loses in
structure.
2
Heat pump
Preheating ~30K;
Heating ~ 45K.
Cross-flow or accumulation
buffer tanks.
All types of heating, low and high
temperature (35ºC and 65ºC). Both
- water and air
borne heating
systems.
As a special case, in buildings with cooling in summer time, extract air can be used for
reversible heat pump heat dissipation, then heat exchanger in air duct is already installed for
heat recovery purposes [ 4].
1.3. Recommendations for indoor air parameters in swimming pools
In modern understanding, a swimming pool - is a hydro-technical construction, intended
for water sports. Usually temperatures maintained in swimming pool halls are between 28ºC
and 32ºC, according to application, preferable 1.1 to 2.2ºC higher than the water temperature.
It is suggested, that the indoor air dew point should be held at least 2.7ºC below the coldest
surface temperature [10]. A little negative air pressure – about 10 Pa is necessary to keep air
out of the rest of the building and out of cold cavities for most of the time.
As a result of a large area of wet surfaces and swimmer’s splashes there are high
moisture loads on the pool room air ventilation and air – conditioning system. Such
maintenance of air parameters as heating and drying, active ventilation and other factors
related to water purification and physical parameters maintenance make this type of buildings
one of the largest energy consumers in public / multipurpose buildings [ 7, 8].
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2. HVAC SYSTEM
The mansion was built in summer 2010 and is located near the Gulf of Riga, the Baltic
Sea. Living and recreation parts of the building are separated. Due to the design specifics, it
was difficult to install classic supply-exhaust ventilation with heat recuperation, and designers
choose to use heat pump for extract air heat utilization. This solution is aimed to provide
energy recovery both in winter and in summer seasons.
The living part of building has decentralized extract ventilation system. The fresh air is
supplying to rooms through the window grilles and is being extracted from washrooms. The
air handling unit (AHU1) is of direct-flow type.
Swimming pool room ventilation is provided by supply – exhaust air handling unit with
internal heat pump (AHU2), which consists of the following elements:
• Supply air water heating coil – to utilize the main heat pump produced heat;
• Supply air water post heating coil – to heat the supply air to the room temperature;
• Internal heat pump – to remove moisture from return air;
• Recirculation section;
• Supply and exhaust fans.
Tables 2 and 3 shows air AHU parameters and legend of the symbols used in schemes
respectively.
Table 2. Air handling unit parameters
Description
AHU1
AHU2
Electrical power of supply / exhaust fans, kW
0.2
0.6 / 0.6
Static pressure supply / exhaust fans, Pa
150
250 / 250
Air flow of supply / exhaust fans,
hm /
3
930
1500 / 1500
Temperature / humidity efficiency of heat exchanger
-
50% / 0%
Heating power of water heating coil, kW
Heating / cooling power of heat utilization coil, kW
-
0 / 4.1
14
12.3 / 0
Table 3. Scheme legend
Symbol
Description
Symbol
Description
-
Fan with frequency converter
-
Temperature / humidity sensor
-
Heating coil
-
Differential pressure gauge
-
Cooling coil
-
Motorized air flow damper
-
Air filter
-
Motorized valve
CYSENI 2011, May 26-27, Kaunas, Lithuania
ISSN 1822-7554, www.cyseni.com
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AHU1 functional scheme is shown in Fig. 1:
Fig. 1 The functional scheme of AHU1
The AHU1 heat recovery coil utilizes extract air energy during winter periods (heat
pump – heating mode). When the heat pump is switching to cooling mode, the motorized
valve is turning off and water flow is redirecting to AHU2 heater.
AHU2 functional scheme is shown in Fig. 2:
Fig. 2 The functional scheme of AHU2
3. METHODS
The building is equipped with minimum energy counters, that is not usable for deeper
research – one gas consumption and electrical consumption counter serves for all the building.
Therefore, to evaluate HVAC system efficiency, we have chosen theoretical method –
building simulation within the with DOE 2.1E core based application (RIUSKA v.4.6.40).
The simulation is performed, using average climate data for Riga, Latvia (the building is
located at a distance approximately 80 km from the Capital of Latvia), from the software
CYSENI 2011, May 26-27, Kaunas, Lithuania
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climatic database. As soon as used program doesn’t allow simulating HVAC equipment with
reversible cycle, it was made two Room models in CAD program and then exported to
simulation software. Room models were transformed to Building Information Models
(BIM’s). The simulation performed for all rooms with activated concrete slabs (heating /
cooling pipes are concreted into the slab, see Fig.3).
Fig. 3 Principal scheme of the activated concrete slab
Living part model is shown in Fig. 4.
Fig. 4 The model of the Living Part
Living part model, which represents a room, the area of windows and walls of which is
the sum of window and wall area in a residential part of the building.
The building envelope characteristics for Living Part are shown in Table 4:
Table 4. The building envelope characteristics for Living Part
Name
A, m²
U, W/m²/°C
Azimuth (°)
Window (m²)
Door (m²)
1
Ground floor
151,7
0,25
2
Roof
151,7
0,16
0
3
EW*
26,7
0,21
90
4,8
4
EW
26,7
0,21
270
5
EW
69,0
0,21
0
54,00
6
EW
69,0
0,21
180
54,00
CYSENI 2011, May 26-27, Kaunas, Lithuania
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*External Wall. Brick-faced concrete external wall 330 mm thick (Concrete 100 mm,
mineral wool 115 mm, wind shield board 30 mm, brick, perforated, 85 mm). Window type:
2xClear, 6+6 mm, Aluminium frames, U=2.78 W/m²/°C, according to project design.
The model of Swimming pool room is made according to the project (Fig. 5).
Fig. 5 The model of Swimming pool room
The area of the pool is 32 m². The water temperature is equal to the room air
temperature (on 1-2ºC lower), so we didn’t take into account heat losses or gains in this area.
Table 5. The building envelope characteristics for Swimming pool Room
Name
A, m²
U, W/m²/°C
Azimuth (°)
Window (m²)
Door (m²)
Swimming pool
1
Ground floor
71,0
0,25
2
Roof
93,0
0,16
0
3
EW
65,5
0,21
180
9,45
4
EW
17,4
0,21
90
5
EW
65,5
0,21
0
40,50
6
EW
17,4
0,21
270
2,40
4. RESULTS
Simulation results show, that Living part consumes 33MWh heating energy per year.
Cooling electricity, with heat pump COP 2.5 is 4 MWh annually, which is much less than the
energy, consumed on heating (Fig. 6).
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0
1
2
3
4
5
6
7
HVAC, fans
0,092
0,083
0,092
0,089
0,092
0,089
0,092
0,092
0,089
0,092
0,089
0,092
HVAC, cooling electr.
0,005
0,007
0,012
0,112
0,477
0,930
1,136
0,950
0,298
0,051
0,006
0,003
Heating
5,715
5,046
4,514
2,855
1,411
0,557
0,342
0,407
1,180
2,311
3,665
5,011
1
2
3
4
5
6
7
8
9
10
11
12
MWh
Fig. 6. HVAC system annual energy consumption in Living Part of the building
Heating energy consumption in Swimming pool is 77,14 MWh per year. Fig.7 shows,
that cooling is not required in this zone, because of high air temperature, maintained all year.
0
2
4
6
8
10
12
HVAC, fans
0,844
0,763
0,844
0,817
0,844
0,817
0,844
0,844
0,817
0,844
0,817
0,844
HVAC, cooling electr.
0,000
0,000
0,000
0,000
0,000
0,000
0,000
0,000
0,000
0,000
0,000
0,000
Heating overall
9,476
8,568
8,265
6,538
5,082
3,867
3,674
3,969
5,020
6,339
7,515
8,826
1
2
3
4
5
6
7
8
9
10
11
12
MWh
Fig. 7. Annual heating energy consumption in swimming pool room
During the cooling period, the amount of heat energy, produced by heat pump, is 15.95
MWh per year. We have summarized Swimming pool room heating demand and heat,
produced by heat pump. Fig. 8 shows the ratio of these two variables:
CYSENI 2011, May 26-27, Kaunas, Lithuania
ISSN 1822-7554, www.cyseni.com
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0
2
4
6
8
10
12
HVAC, fans
0,844
0,763
0,844
0,817
0,844
0,817
0,844
0,844
0,817
0,844
0,817
0,844
Heat pump, heating
0,027
0,036
0,061
0,561
2,385
3,867
3,674
3,969
1,491
0,256
0,028
0,016
Heating with heat pump preheat
9,449
8,532
8,203
5,977
2,697
0,170
0,080
0,270
3,529
6,083
7,487
8,810
1
2
3
4
5
6
7
8
9
10
11
12
MWh
Fig. 8. Annual heating energy consumption in swimming pool room with heat pump produced
energy
In both cases, HVAC fan electricity is less or more constant during the year period.
Small variations are explained by the number of month days fluctuations.
5. DISCUSSION
The main advantage of the described system is that it provides heat utilization during the
summer period. This method is most applicable for building with swimming pools, or other
types of warm water storages. Although, heat pump produced heat within the summer period
can be used in hot-water pre-heating in building with decentralized water supply, as well as in
special-purpose buildings, for example, factories. The highest precision of data obtained could
be achieved, if simulation will include condensation in extract air heat recovery coil. Heat
losses caused by water evaporation from swimming pool surface also should give some
corrections to the results. However, this factor highly depends on the using intensity of
swimming pool [ 8, 10]. The current research focuses on the efficiency of the HVAC system
studied. However, further investigations could be dedicated to evaluations of economical
aspects in similar systems.
6. CONCLUSIONS
The annual energy consumption simulation is made within the average Latvian
meteorological year. Two building’s information models (BIM) were created, according to
existing site design specifics. Simulation results show, that swimming pool room consumes
77 MWh of heating energy per year, the design value is 85 MWh. When heat pump gained
energy is used to preheat swimming pool supply air, annual heat energy consumption
decreases to 62 MWh, which means about 20% saving. The paper results can be useful for
architects and HVAC system designers in other multipurpose buildings with indoor
swimming pools design as an another opportunity to increase the energy efficiency of
building heating, ventilation and air-conditioning systems.
7. REFERENCES
1. LBN 208 08. Multi-storey residential buildings. Latvian building code. Riga, 2008.
CYSENI 2011, May 26-27, Kaunas, Lithuania
ISSN 1822-7554, www.cyseni.com
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2. LVS EN 15251:2007. Indoor environmental input parameters for design and assessment
of energy performance of buildings addressing indoor air quality, thermal environment,
lightning and acoustic. Latvian standard. Riga, 2007.
3. An Nguyen, Youngil Kim, Younggy Shin. Experimental study of sensible heat recovery
of heat pump during heating and ventilation. International Journal of Refrigeration, 2004,
Vol. 28, Elsevier Ltd and IIR, 11 p.
4. R.J. Goldstein et.al. Heat transfer – a review of 2000 literature. International Journal of
Heat and Mass Transfer, 2002. Vol. 45, 105 p.
5. S. Nowotny. Possibilities of improving the thermodynamic working conditions of heat
pumps for heat recovery. International Journal of Refrigeration, Volume 2, Issue 3, May
1979, Pages. 171-175
6. S. B. Riffat and M. C. Gillott. Performance of a novel mechanical ventilation heat
recovery heat pump system. Applied Thermal Engineering Volume 22, Issue 7, May 2002,
Pages 839-845
7. Lewis G. Harriman III, G.W. Brundrett, R. Kittler. Humidity Control Design Guide For
Commercial and Industrial Buildings. Atlanta: ASHRAE, 2001. 180 p. ISBN 978-
1883413989
8. Krumins A., Pelite U., Brahmanis A., et.al. Optimal control strategy of air handling unit
for different microclimates in working and swimming areas of a swimming pool hall.
Indoor Air 2008. Proceedings of the 11th International Conference on Indoor Air Quality
and Climate. [CD]. 2008 August 17-22.
9. VDI 2089-1:2006-09. Technische Gebäudeausrüstung von Schwimbädern – Hallenbäder.
Dutch standard. Berlin, 2009.
10. American Society of Heating, Refrigerating and Air-Conditioning Engineers. ASHRAE
Handbook: Applications SI Edition, Atlanta: ASHRAE, 2004. 400 p. ISBN 1-931862-23-
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