The Preliminary Research of Sea Water District Heating and Cooling for Tallinn Coastal Area

doi:10.4236/sgre.2012.33034

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Smart Grid and Renewable Energy, 2012, 3, 246-252

http://dx.doi.org/10.4236/sgre.2012.33034 Published Online August 2012 (http://www.SciRP.org/journal/sgre)

The Preliminary Research of Sea Water District Heating

and Cooling for Tallinn Coastal Area

Allan Hani, Teet-Andrus Koiv

Environmental Department, Tallinn University of Technology, Tallinn, Estonia.

Email: [email protected]

Received May 2nd, 2012; revised June 1st, 2012; accepted June 8th, 2012

ABSTRACT

This paper describes possibilities to utilize sea water for district heating an d coo ling purp oses in Tallinn co stal area. Th e

sea water temperature profiles and suitability of heating and coo ling generation are studied for continental climatic con-

ditions. The district network study bases on 21 buildings located near to the Gulf of Finland. Industrial reversible heat

pump technology is selected to cover heating and cooling loads for the new buildings. Combination of existing district

heating and h eat pump technology is con sidered for existin g buildings. The results show possibilities, threats and need

for further research of the sea water based heat pump district network implementation.

Keywords: District Heating; Cooling; Sea Water; Heat Pump; Renewable Energy; Office Building

1. Introduction

The European Union 20-20-20 targets emphasize imple-

mentation of renewable energy sources in member states

energy balances. Sea water is a large renewable energy

source, which can be combined with reversible heat

pump technology to produce both thermal and cooling

energy. The working principle is similar to geothermal

energy production, but th e sea water allows utilization of

free cooling during spring and autumn period. The heat

pump technology is studied widely around the World. A

comprehensive review of heat pump systems implemen-

tation possibilities in different fields and also recent im-

provement with coefficient of performance (COP) is

presented [1]. The heat pump technology rapid growth in

200 5 -2 0 1 0 is do c u me nted [2,3]. The sea water elec trically

driven heat pump technology feasibility is compared with

conventional district heating, in case the network radius

is less than 5 km [4]. The calculation includes coal-fired

plants electricity production losses and pumping costs.

When the electricity is produced from natural gas, the

radius degreases. Feasibility of different district heating

and cooling production options is studied [5]. The life

cycle costs are included (installation, system operating,

maintenance costs). The sea water district heating and

cooling is 1.5 times more expensive in China, due to

relatively low coal-produced electrical energy price. All

the economic calculations shall be carried out project by

project separately. Indirect sea water cooling for Japan

commercial buildings is researched [6]. Thermal storage

tank of 4500 m3 is used. Storage tank covers 32% of the

cooling peak load. Difference of water temperature utili-

zation is 7 K (5˚C - 12˚C). Cooling capacity of chillers is

2.3 MW. Large advantage in maintenance costs was

found also a slight saving in initial cost was found. Boiler

plant and heat pump technology is compared by quasi-

dynamic energy-saving calculation [7]. The static calcu-

lations authors presented earlier the same year (2010)

underestimated the feasibility of sea water district heat-

ing and cooling by 20%. Similar study was carried out in

Japan [8]. Compared to conventional systems (cooling

tower and heating boiler plant) the saving of 29% was

received for district cooling and 5% for district heating.

In Swed en the short an d long term impacts of heat pump

technology are compared with district heating systems

[9]. Totally 6 TWH thermal energy was produced in

Sweden year 2007. Energy optimization tool MODEST

was used for systems modelling. In a total thermal en-

ergy balance of Sweden, still the heat pump systems for

district heating will be developed in small scale, com-

bined heat and power from renewable energy resources

(CHP) is preferred. Nevertheless, in our Estonian case

the share of cooling energy of selected buildings is

higher than thermal energy. Therefore in certain costal

areas the free cooling from sea water could be feasible

and ecologically friendly. In Germany the de-nucleari-

zation as a process is started [10]. Renewable energy

storage and transportation possibilities are presented in

the article. The problems are laid on the table, but solu-

tions are still fully open. In Greece the cooling dominates

The Preliminary Research of Sea Water District Heating and Cooling for Tallinn Coastal Area 247

widely over the heating demand [11]. The proposed sys-

tems are vice versa to ours solutions—extra cooling tow-

ers are used to cover peak cooling loads. Heating and

average cooling demand is proposed to be produced with

heat pumps. Groundwater open loop heat pump systems

are researched [12]. Water storage tank is used either on

chilled water or groundwater side. In chilled water side

10% saving was received due to better COP. The study

of environmental impacts of different heat sources (coal

boiler, gas boiler and heat pump with different COP) [13].

All the heat pumps with COP > 2.5 are more environ-

mentally friendly to install than gas boilers. The coal

boilers should be avoided. Low temperature heating will

give better COP [14]. In our sea water district heating

and cooling case the new buildings shall have low tem-

perature heating and in existing buildings the high tem-

perature district heating will be combined with heat

pump system. Different connection possibilities are pre-

sented in research of combining existing district heating

and new heat pump technology [15]. The heat pu mp heat

exchangers optimization study [16] gives a comprehen-

sive overview of the heat exchanger selection principles.

Different new implementation options and heat pump

refrig erants are presented in exhaustive articles [17-23].

The feasibility and technical possibilities are closely

related to different boundary parameters:

1) Sea water temperature profile and salinity;

2) Outdoor climatic conditions;

3) Coastal area geology;

4) Possibilities to construct the sea water and district

network pi pel ines;

5) Heating and cooling loads of the connectable build-

ings;

6) Temperature regimes of the pipelines;

7) Secu re energy supply.

In current study these different aspects are analysed.

The threats and possibilities are presented of the sea wa-

ter district heating and cooling for Tallinn coastal area.

2. Methods

2.1. Gulf of Finland Parameters

The water and thermal processes in Gulf of Finland are

continuously monitored among HELCOM project. Sci-

entific articles [24,25] are written about the sea water

parameters by Scandinavian and Estonian scientists.

All the measurements reported to HELCOM have to

comply with survey program COMBINE requirements.

The information about requirements is available:

http://www.helcom.fi/groups/monas/CombineManual/en

GB/main/

Due to the salinity of the gulf water the ice formation

will appear <–0.4˚C.

Average ice thickness is 31 cm, very rare thickness >

50 - 60 cm (absolute maximum 1.2 m in a 150 years).

The sea water temperature and profile are analysed for

the sea water heat pump plant possibility. The average

depth profile of Gulf of Finland is presented in Table 1.

Depth of the gulf is shallow—averagely it will in-

crease 5 m by additional distance of 1 km from the coast.

Economically it would be efficient to search deeper loca-

tions in costal area (<500 m). In following Figure 1 the

sea water temperature profile during the year is presented.

The data bases on Gulf of Finland monitoring station F3

info. Monthly average as well minimum and maximum

temperatures are presented in correlation of sea depth.

There is a wide variation of temperature during the

year in a whole depth profile. In combination of distance

<500 m and depth –20 m the temperature range will be

between –0.31 ˚C in winter to 16.6˚C in summer.

2.2. Outdoor Climatic Conditions

Tallinn area external air duration diagram is presented in

Figure 2.

In our case outdoor climatic conditions and other ref-

erence buildings design information is taken as a basis

for dimensioning the sea water district heating and cool-

ing plant loads. Minimum temperature for heating load

calculation is –22˚C to assure 21˚C in build ings. Cooling

load design parameters are +27˚C and 50% relative hu-

midity to assure +24˚C in buildings.

Table 1. Average gulf of Finland depth profile .

Distance from coast

m Depth (sea)

500 20

1500 25

3200 30

4000 35

5500 40

Figure 1. Monitoring station F3 measurement results.

The Preliminary Research of Sea Water District Heating and Cooling for Tallinn Coastal Area

248

3. Results and Discussion

3.1. Case Study

Based on the local area development plan 21 buildings

(see Table 2) are included to the research from Port of

Tallinn area. There are existing buildings, but a majority

is considered to be erected. The heating and cooling

consumption total network is planned <1 km radius from

the coast.

In preliminary stage 80 W/m2 public area for heating

load calculations and 100 W/m2 public area for cooling

calculations was calculated. These values include trans-

portation losses 5% for cooling and 10% for thermal en-

ergy. 60 W/m2 public area is calculated for Building no

17 cooling demand.

Total 14.3 MW heating and 16.4 MW cooling load is

calculated. Simultaneous factor of 0.85 is applied to the

calculation results. The plant maximum thermal capacity

is 12 MW and cooling capacity 14 MW. Plant shall be

located beside Gulf of Finland

The Tallinn costal area depth profile is presented in

following Figure 3. The depth of 25 m is located 500 m

from the area. Flow pipe shall be directed there. Return

pipe can be located near to the coast. Figure 2. Tallinn external air duration diagram.

Table 2. Heating and cooling load calculation.

Building

no Building height

m Storeys above

ground Public area

m2 Cooling demand

kW Heating demand

1 24 6 8764 876 701

2 24 6 18,870 1887 1510

3 24 6 1458 146 117

4 24 6 3564 356 285

5 24 6 5780 578 462

6 18 5 5198 520 416

7 11 2 2340 234 187

8 18 5 8775 878 702

9 24 6 2268 227 181

10 24 6 2430 243 194

11 24 6 10,260 1026 821

12 24 6 5049 505 404

13 24 6 4860 486 389

14 20 5 24,500 2450 1960

15 16 4 4250 425 340

16 19 5 11,200 1120 896

17 - 4 37,221 2233 2978

18 19 5 10,500 1050 840

19 19 5 2200 220 176

20 19 5 5250 525 420

21 22 5 3700 370 296

The Preliminary Research of Sea Water District Heating and Cooling for Tallinn Coastal Area 249

Figure 3. Tallinn coastal area sea water profile.

Figure 4. The principle schematic of sea er district heating and cooling plant. wat

Current Distortion Evaluation in Traction 4Q Constant Switching Frequency Converters

250

3.2. Technology

Two industrial heat pumps (e.g. Uniturbo 34FY a´8.0

MW) with high condenser water outlet temperatures for

heating and with cooling operation are considered to

cover the heating and cooling demand of the buildings.

The principle schematic is presented in Figure 4.

3.2.1. Heati ng Mode Opera tion

Supply water temperature to district network 60˚C - 90˚C

(70˚C).

Return water temperature from district network 50˚C.

Thermal storage tank is to provide district heating

network temperature stability and prevent freezing of the

evaporator side of return sea water. 3600 m3 tank could

provide up to 7 days thermal energy (DT = 20 K) .

Sea water DT = 2 K (0˚C/2˚C).

The new buildings must be deigned for low tempera-

ture heating (55˚C/40˚C) to allow max efficiency of the

heat pump plant. For existing buildings (80˚C/60˚C or

70˚C/50˚C) combination of heat pump plant and district

heating shall be considered.

District heating network shall be insulated to provide

minimum thermal losses of the system.

3.2.2. Cool i ng Mode Operation

Supply water temperature to district network 5˚C. Return

water temperature from district network 15˚C - 20˚C.

Sea water temperature < 4˚C.

Completely free-cooling;

Sea water temperature 4˚C - 10˚C.

Pre-cooling with sea water + compressor cooling;

Sea water temperature > 10˚C.

Only compressor cooling (free cooling heat exchangers

are equipped with bypasses).

Due to fact that summer period soil temperature in 1.5

m depth is 10˚C it is not necessary to insulate the return

pipe of the district cooling network. Supply pipe is insu-

lated with 10 cm nowadays heat insulation material.

The titanium heat exchangers allow usage of the soft

water in distribution network while problematic salty sea

water handling will be done in open central circuit.

3.3. Comparable Research and Risk Definition

Based on the reference projects studied and referred in

introduction part of current study the sea water for district

heating and cooling is a favourable renewable energy

source. Still there are several matters to be considered

before the real investment decis i on co ul d be made.

Environmental impact study is required before any of

the projects will be executed. In addition to evaluation of

the deep zone cold water pumping, the analysis of recy-

cling the sea water back to lower sea water zone with

higher and lower temperatures should be carried out.

Possibilities to use old underground tunnels, etc. must

be studied to find economically reasonable solutions for

district network construction.

The thermal storage tank size op timization is necessary

to do as it affects both the stability of the district heating

network and eco nomical possibilities to contin ue with the

combined plant design.

There is a risk to have too low temperatures in evapo-

ration side during cold winter period which will cause

shut-off the heat pumps. A storage tank helps to over-

come this, but can not fully prevent it, if the cold period

will last longer than designed. The design parameters

must be carefully considered.

Also minimum altitudes between heat exchangers and

water resource le vel sho uld be designed.

Centralized district heating and cooling plant, heat ex-

changers, pumping station is normally less expensive

than decentralised systems altogether.

Centralized system has less maintenance problems.

Usually conventional cooling systems utilize electrical

energy, which in Estonia is produced from oil-shale. Sea

water is a huge cold water resource, so free cooling can

be used.

4. Conclusions

In the current study possibilities of sea water utilization

as thermal and cooling energy resource are studied in

continental climate area. The Gulf of Finland as well as

Tallinn outdoor climate parameters were taken to inputs

for the study.

There are 21 office buildings selected from real devel-

opment project with 14 MW cooling and 12 MW heating

energy dema nd.

Possible connection diagram is presented for the

buildings. The most important concern is to provide

thermal energy also in low sea water temperature condi-

tions, where the return glycol-water mixture from heat

pump can cause sea water to freeze inside the heat ex-

changer. The selection of sea water pipes routing shall be

studied in future to provide more the most effective con-

ditions. Also closed-loop pipe system shall be studied to

prevent the freezing problem (glycol-water mixture in-

side the piping).

Low temperature (55˚C/40˚C) heating shall be design-

ed for new buildings. For existing buildings the new dis-

trict heating system must be combined with old city dis-

trict heating network.

The summer period district co oling solution is simpler.

Three possible control modes are applied—free cooling is

preferred and automation system shall be designed ac-

cording to this requirement.

The parallel heating and cooling operation mode can

be applied with 2 heat pumps. It is important mostly in

spring and autumn season, where different buildings and

The Preliminary Research of Sea Water District Heating and Cooling for Tallinn Coastal Area 251

even building sides can have both, cooling and heating

demand.

The optimization of systems and economical feasibility

study should be carried out before to continue with re-

search and real design. Furthermore, trigeneration versus

sea water district heating and cooling evaluation is

needed to be researche d.

5. Acknowledgements

Estonian Ministry of Education and Research is greatly

acknowledged for funding and supporting this study.

European Social Foundation financing task 1.2.4 Coop-

eration of Universities and Innovation Development,

Doctoral School project “Civil Engineering and Envi-

ronmental Engineering” code 1.2.0401.09-0080 has made

publishing of this article possible.

REFERENCES

[1] K. J. Chua, S. K. Chou and W. M. Yang, “Advantages in

Heat Pump Systems: A Review,” Applied Energy, Vol. 87,

No. 12, 2010, pp. 3611-3624.

doi:10.1016/j.apenergy.2010.06.014

[2] J. W. Lund, D. H. Freeston and T. L. Boyd, “Direct Ap-

plication of Geothermal Energy: 2005 Worldwide Re-

view,” Geothermics, Vol. 34, No. 6, 2005, pp. 691-727.

doi:10.1016/j.geothermics.2005.09.003

[3] J. W. Lund, D. H. Freeston and T. L. Boyd, “Direct Utili-

zation of Geothermal Energy 2010 Worldwide Review,”

Geothermics, Vol. 40, No. 3, 2010, pp. 159-180.

doi:10.1016/j.geothermics.2011.07.004

[4] H. W. Shu, D. M. Lin, X. L. Li and Y. X. Zhu, “En-

ergy-Saving Judgment of Electric-Driven Seawater Source

Heat Pump District Heating System over Boiler House

District Heating System,” Energy and Buildings, Vol. 42,

No. 6, 2010, pp. 889-895.

doi:10.1016/j.enbuild.2010.01.001

[5] H. W. Shu, D. M. Lin, C. H. Zhang and Y. X. Zhu,

“Study on the Decision-Making of District Cooling and

Heating Systems by Means of Value Engineering,” Re-

newable Energy, Vol. 35, No. 9, 2010, pp. 1929-1939.

doi:10.1016/j.renene.2010.01.021

[6] Y.-H. Song, Y. Akashi and J.-J. Yee, “Effects of Utilizing

Seawater as a Cooling Source System in a Commercial

Complex,” Energy and Buildings, Vol. 39, No. 10, 2007,

pp. 1080-1087. doi:10.1016/j.enbuild.2006.11.011

[7] H. W. Shu, D. M. Lin, X. L. Li and Y. X. Zhu,

“Quasi-Dynamic Energy-Saving Judgment of Electric-

Driven Seawater Source Heat Pump District Heating Sys-

tem over Boiler House District Heating System,” Energy

and Buildings, Vol. 42, No. 12, 2010, pp. 2424-2430.

doi:10.1016/j.enbuild.2010.08.012

[8] T. Nagota, Y. Shimoda and M. Mizuno, “Verification of

the Energy-Saving Effect of the District Heating and

Cooling System-Simulation of an Electric-Driven Heat

Pump System,” Energy and Buildings, Vol. 40, No. 5,

2008, pp. 732-741. doi:10.1016/j.enbuild.2007.05.007

[9] M. Eriksson and L. Vamling, “Future Use of Heat Pumps

in Swedish District Heating Systems: Short- and Long-

Term Impact of Policy Instruments and Planned Invest-

ments,” Applied Energy, Vol. 84, No. 12, 2007, pp. 1240-

1257. doi:10.1016/j.apenergy.2007.02.009

[10] C.-J. Winter, “After Nuclear Has Gone: Energy in Ger-

many,” International Journal of Hydrogen Energy, Vol.

37, No. 1, 2012, pp.1-5.

doi:10.1016/j.ijhydene.2011.08.001

[11] Z. Sagia, C. Rakopoulos and E. Kakaras, “Cooling Domi-

nated Hybrid Ground Source Heat Pump System Applica-

tion,” Applied Energy, Vol. 94, 2012, pp. 41-47.

doi:10.1016/j.apenergy.2012.01.031

[12] S. L. Russo, G. Taddia, G. Baccino and V. Verda, “Dif-

ferent Design Scenarios Related to an Open Loop

Groundwater Heat Pump in a Large Building: Impact on

Subsurface and Primary Energy Consumption,” Energy

and Buildings, Vol. 43, No. 2-3, 2011, pp. 347-357.

doi:10.1016/j.enbuild.2010.09.026

[13] C. M. Chen, Y. F. Zhang and L. J. Ma, “Assessment for

Central Heating Systems with Different Heat Sources: A

Case Study,” Energy and Buildings, Vol. 48, 2012, pp.

168-174. doi:10.1016/j.enbuild.2012.01.025

[14] V. Verda, G. Baccino, A. Sciacovelli and S. L. Russo,

“Impact of District Heating and Groundwater Heat Pump

Systems on the Primary Energy Needs in Urban Areas,”

Applied Thermal Engineering, Vol. 40, 2012, pp. 18-26.

doi:10.1016/j.applthermaleng.2012.01.047

[15] Y. Wang and Y. F. Zhang, “Analysis of the Dilatancy

Technology of District Heating System with High-Tem-

perature Heat Pump,” Energy and Buildings, Vol. 47,

2012, pp. 230-236. doi:10.1016/j.enbuild.2011.11.038

[16] B. David, J. Ramousse and L. G. Luo, “Optimization of

Thermoelectric Heat Pumps by Operating Condition

Management and Heat Exchanger Design,” Energy Con-

version and Management, Vol. 60, 2012, pp. 125-133.

doi:10.1016/j.enconman.2012.02.007

[17] S. Okamoto, “A Heat Pump System with a Latent Heat

Storage Utilizing Seawater Installed in an Aquarium,”

Energy and Buildings, Vol. 38, No. 2, 2006, pp. 121-128.

doi:10.1016/j.enbuild.2005.04.004

[18] K. Bakirci and B. Yuksel, “Experimental Thermal Per-

formance of a Solar Source Heat-Pump System for Resi-

dential Heating in Cold Climate Region,” Applied Ther-

mal Engineering, Vol. 31, No. 8-9, 2011, pp. 1508-1518.

doi:10.1016/j.applthermaleng.2011.01.039

[19] K. Hirata and H. Kakiuchi, “Energy Saving for Ethylene

Process by Adsorption Heat Pump,” Applied Thermal En-

gineering, Vol. 31, No. 13, 2011, pp. 2115-2122.

doi:10.1016/j.applthermaleng.2011.03.031

[20] W. E. TeGrotenhuis, P. H. Humble and J. B. Sweeney,

“Simulation of a High Efficiency Multi-Bed Adsorption

Heat Pump,” Applied Thermal Engineering, Vol. 37, 2012,

pp. 176-182. doi:10.1016/j.applthermaleng.2011.11.012

[21] B. T. Austin and K. Sumathy, “Transcritical Carbon Di-

oxide Heat Pump Systems: A Review,” Renewable and

Sustainable Energy Reviews, Vol. 15, No. 8, 2011, pp.

4013-4029. doi:10.1016/j.rser.2011.07.021

[22] K. Yasukawa and S. Takasugi, “Present Status of Under-

The Preliminary Research of Sea Water District Heating and Cooling for Tallinn Coastal Area

252

ground Thermal Utilization in Japan,” Geothermics, Vol.

32, No. 4-6, 2003, pp. 609-618.

doi:10.1016/j.geothermics.2003.07.011

[23] A. Hall, J. A. Scott and H. Shang, “Geothermal Energy

Recovery from Underground Mines,” Renewable and Sus-

tainable Energy Reviews, Vol. 15, No. 2, 2011, pp. 916-

924. doi:10.1016/j.rser.2010.11.007

[24] B. Jonsson, K. Doos, J. Nycander and P. Lundberg,

“Standing Waves in the Gulf of Finland and Their Rela-

tionship to the Basin-Wide Baltic Seiches,” Journal of Ge o -

physical Research, Vol. 113, 2008, Article ID: C03004.

doi:10.1029/2006JC003862

[25] T. Liblik and U. Lips, “Characteristics and Variability of

the Vertical Thermohaline Structure in the Gulf of Finland

in Summer,” Boreal Environment Research, Vol. 16, 2011,

pp. 73-83.