Smart Grid and Renewable Energy, 2012, 3, 246-252 Published Online August 2012 (
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.
Received May 2nd, 2012; revised June 1st, 2012; accepted June 8th, 2012
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
Copyright © 2012 SciRes. SGRE
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-
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:
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.
Copyright © 2012 SciRes. SGRE
The Preliminary Research of Sea Water District Heating and Cooling for Tallinn Coastal Area
Copyright © 2012 SciRes. SGRE
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.
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
Copyright © 2012 SciRes. SGRE
Current Distortion Evaluation in Traction 4Q Constant Switching Frequency Converters
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
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
Copyright © 2012 SciRes. SGRE
The Preliminary Research of Sea Water District Heating and Cooling for Tallinn Coastal Area 251
even building sides can have both, cooling and heating
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.
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