The <str<strong>on</strong>g>12th</str<strong>on</strong>g> <str<strong>on</strong>g>Internati<strong>on</strong>al</str<strong>on</strong>g> <str<strong>on</strong>g>Symposium</str<strong>on</strong>g> <strong>on</strong> <strong>District</strong> <strong>Heating</strong> <strong>and</strong> <strong>Cooling</strong>,September 5 th to September 7 th , 2010, Tallinn, Est<strong>on</strong>iawhen the supply temperature <strong>on</strong> primary side droppedtoo low (< 65 °C). The valve allowed a c<strong>on</strong>stant massflow (0.015 kg/s) to go past the heat exchanger <strong>on</strong> theprimary side. This soluti<strong>on</strong> helped the situati<strong>on</strong>significantly although not without ill effects as can beseen from the heat losses presented below.The use of a by-pass valve to ensure the appropriatetemperature level for domestic hot water also meanhigher heat losses <strong>and</strong> pumping power <strong>and</strong> effectivelylower cooling; all of which are undesirable outcomes.One possibility to solve the problem is just to accept theflaw <strong>and</strong> to use additi<strong>on</strong>al electrical heating element toraise the temperature of domestic hot water to therequired level. As the temperature boost needed is formost of the time quite small <strong>and</strong> is <strong>on</strong>ly needed insummertime, the increase in electricity c<strong>on</strong>sumpti<strong>on</strong> isreas<strong>on</strong>able.Because of the high capital costs of district heating, thepipes should basically be sized as tight as possiblewhile keeping in mind the future dem<strong>and</strong> for the pipelinein questi<strong>on</strong>. As the pipes are small, the volume of waterc<strong>on</strong>tained is also low. This leads to water cooling morerapidly than in larger pipes. The Figure 4 illustrates thiswith a simplified example by showing the temperature<strong>on</strong> supply side service pipes if there is no flow for threedifferent pipe sizes. The temperature drop of 15 °C, forexample, takes 5 times l<strong>on</strong>ger with a pipe size DN 50than with a small DN 15 pipe. The calculati<strong>on</strong>s assumea c<strong>on</strong>stant return side temperature of 30 °C <strong>and</strong> aground temperature of 5 °C.Temperature (°C)70605040302010DN 15 DN 25 DN 5000 2 4 6 8Time (h)Figure 4. Temperature drop in three pipe sizes when noflow is introduced.The use of smaller pipes reduces the heat losses inW/m <strong>and</strong> this is accentuated if the temperature leveldrops as described above. As a result, looking solely <strong>on</strong>heat losses when designing a low heat density areanetwork <strong>on</strong> comm<strong>on</strong> design principles can lead toreliability issues as the system cannot supply the heatrequired by the c<strong>on</strong>sumers.The relative heat losses (that is, heat losses per neededproducti<strong>on</strong>) for the simulated case are 13.8 % in a year.The m<strong>on</strong>thly values can be seen in Figure 5. While the71relative heat losses in the heating seas<strong>on</strong> areacceptable, they reached 47 % in the summertime. Thehigh heat losses are partly because of the by-pass valveletting hot water past the heat exchangers. The by-passvalve is also resp<strong>on</strong>sible for small cooling, i.e. thedifference between supply <strong>and</strong> return temperatures,within the system in summertime (Figure 6).Relative heat losses (-)1.00.90.80.70.60.50.40.30.20.10.0I II III IV V VI VII VIII IX X XI XIIM<strong>on</strong>thFigure 5. M<strong>on</strong>thly relative heat losses.<strong>Cooling</strong> (°C)90807060504030201000 50 100 150 200 250 300 350DaysFigure 6. Difference between supply <strong>and</strong> returntemperatures at the border of the area.The most obvious way to cut heat losses in alreadyreas<strong>on</strong>able insulated network is to lower the supplytemperature. In the simulated system, this would causeproblems because aforementi<strong>on</strong>ed issues c<strong>on</strong>cerningdomestic hot water dem<strong>and</strong> in summertime, <strong>and</strong> duringthe heating seas<strong>on</strong> because of the traditi<strong>on</strong>al radiatorheating design temperatures of 70/40 °C. However, ifmore significant changes would be possible, a floorheating system <strong>and</strong> a heat pump coupled with anaccumulator h<strong>and</strong>ling the higher temperature levelrequired domestic hot water would enhance theefficiency of the distributi<strong>on</strong> system at a price of a verymodest increase in electricity c<strong>on</strong>sumpti<strong>on</strong> <strong>and</strong> higherinvestment costs for the c<strong>on</strong>sumer because of theaccumulator, heat pump <strong>and</strong> floor heating. If thedomestic hot water dem<strong>and</strong> takes 3.75 MWh/year,20 percent of the total c<strong>on</strong>sumpti<strong>on</strong> of 18.75 MWh/year,the electricity c<strong>on</strong>sumpti<strong>on</strong> would be a very reas<strong>on</strong>able
The <str<strong>on</strong>g>12th</str<strong>on</strong>g> <str<strong>on</strong>g>Internati<strong>on</strong>al</str<strong>on</strong>g> <str<strong>on</strong>g>Symposium</str<strong>on</strong>g> <strong>on</strong> <strong>District</strong> <strong>Heating</strong> <strong>and</strong> <strong>Cooling</strong>,September 5 th to September 7 th , 2010, Tallinn, Est<strong>on</strong>ia1.25 MWh with an average COP of 3. With this setup,supply temperature would need to be just 40 °C.CONCLUSIONSThe use of traditi<strong>on</strong>al district heating network designprinciples can lead to an inefficient area heating systemin areas with low heat density. Special attenti<strong>on</strong> must bepaid <strong>on</strong> operati<strong>on</strong> of the system to ensure reliability, <strong>on</strong>eof the advantages of district heating.When aiming for an efficient system, <strong>on</strong>e goal is tominimize the heat losses. However, c<strong>on</strong>centrating solely<strong>on</strong> this can make another problem, maintaining highenough temperature level for domestic hot water insummertime, even worse. The problem can be solvedusing a by-pass valve, but this causes unwantedeffects; worse cooling <strong>and</strong> an increase in heat losses<strong>and</strong> pumping power. Other soluti<strong>on</strong>s are auxiliaryheating (electrical heating or a heat pump) or the use ofan accumulator <strong>and</strong> with it, aiming for a steady domestichot water load.REFERENCES[1] Lappeenranta University of Technology,Kaukolämpöjohtojen optimaalisen eristyspaksuudentarkastelu / Investigati<strong>on</strong> of the optimalinsulati<strong>on</strong> thickness <strong>on</strong> district heating pipes,Energy Industry, 2009, 36 p.[2] Preinsulated district heating pipes,Recommendati<strong>on</strong> L1/2010, Energy Industry, 2010,44 p.[3] Zinko, H., Bøhm, B., Kristjanss<strong>on</strong>, H., Ottos<strong>on</strong>, U.,Rämä, M., Sipilä, K., <strong>District</strong> heating distributi<strong>on</strong> inareas with low heat dem<strong>and</strong> density, IEA DHCAnnex VIII, 2008, 117 p.[4] Ikäheimo, J., Söderman, J., Petters<strong>on</strong>, F., Ahtila, P.,Keppo, I., Nuorkivi, A., Sipilä, K. 2005. DO2DES– Design of Optimal Distributed Energy Systems,Design of district heating network. Åbo Akademi.Report 2005-1.Another approach is lower the supply temperaturesignificantly <strong>and</strong> to use floor heating <strong>and</strong> heat pump withan accumulator for domestic hot water dem<strong>and</strong>. This isnot suitable for existing areas with a heating systemalready designed, but for new areas it is a reas<strong>on</strong>able<strong>and</strong>, compared to the traditi<strong>on</strong>al district heating design,an efficient way to provide heating.72
- Page 1:
12th Inter
- Page 5 and 6:
The 12th I
- Page 7 and 8:
The 12th I
- Page 10 and 11:
The 12th I
- Page 12 and 13:
The 12th I
- Page 14 and 15:
For the case of parallel buried pip
- Page 16 and 17:
The 12th I
- Page 18 and 19:
The 12th I
- Page 20 and 21:
The 12th I
- Page 22 and 23: The 12th I
- Page 24 and 25: The 12th I
- Page 26 and 27: The 12th I
- Page 28 and 29: The 12th I
- Page 30 and 31: The 12th I
- Page 32 and 33: The 12th I
- Page 34 and 35: The 12th I
- Page 36 and 37: The 12th I
- Page 38 and 39: The 12th I
- Page 40 and 41: The 12th I
- Page 42 and 43: The 12th I
- Page 44 and 45: The 12th I
- Page 46 and 47: The 12th I
- Page 48 and 49: The 12th I
- Page 50 and 51: The 12th I
- Page 52 and 53: The 12th I
- Page 54 and 55: The 12th I
- Page 56 and 57: The 12th I
- Page 58 and 59: The 12th I
- Page 60 and 61: The 12th I
- Page 62 and 63: The 12th I
- Page 64 and 65: The 12th I
- Page 66 and 67: The 12th I
- Page 68 and 69: The 12th I
- Page 70 and 71: The 12th I
- Page 74 and 75: The 12th I
- Page 76 and 77: The 12th I
- Page 78 and 79: The 12th I
- Page 80 and 81: The 12th I
- Page 82 and 83: The 12th I
- Page 84 and 85: The 12th I
- Page 86 and 87: The 12th I
- Page 88 and 89: The 12th I
- Page 90 and 91: The 12th I
- Page 92 and 93: The 12th I
- Page 94 and 95: The 12th I
- Page 96 and 97: The 12th I
- Page 98 and 99: the street the more shallow the sha
- Page 100 and 101: The 12th I
- Page 102 and 103: The 12th I
- Page 104 and 105: The 12th I
- Page 106 and 107: The 12th I
- Page 108 and 109: The 12th I
- Page 110 and 111: P-1P-4P-9P-7E-5P-14P-8The 1
- Page 112 and 113: The 12th I
- Page 114 and 115: The 12th I
- Page 116 and 117: The 12th I
- Page 118 and 119: The 12th I
- Page 120 and 121: The 12th I
- Page 122 and 123:
The 12th I
- Page 124 and 125:
The 12th I
- Page 126 and 127:
The 12th I
- Page 128 and 129:
The 12th I
- Page 130 and 131:
The 12th I
- Page 132 and 133:
The 12th I
- Page 134 and 135:
The 12th I
- Page 136 and 137:
The 12th I
- Page 138 and 139:
to heating costs of 14,5 ct/kWh. Th
- Page 140 and 141:
The 12th I
- Page 142 and 143:
The 12th I
- Page 144 and 145:
The 12th I
- Page 146 and 147:
The 12th I
- Page 148 and 149:
academic access is facilitated as t
- Page 150 and 151:
The 12th I
- Page 152 and 153:
The 12th I
- Page 154 and 155:
The 12th I
- Page 156 and 157:
The 12th I
- Page 158 and 159:
The 12th I
- Page 160 and 161:
The 12th I
- Page 162 and 163:
1. CHP system operation in A2. Ther
- Page 164 and 165:
The 12th I
- Page 166 and 167:
is covered by operating HOB. In oth
- Page 168 and 169:
The 12th I
- Page 170 and 171:
The 12th I
- Page 172 and 173:
The 12th I
- Page 174 and 175:
The 12th I
- Page 176 and 177:
The 12th I
- Page 178 and 179:
The 12th I
- Page 180 and 181:
The 12th I
- Page 182 and 183:
The 12th I
- Page 184 and 185:
The 12th I
- Page 186 and 187:
The 12th I
- Page 188 and 189:
The 12th I
- Page 190 and 191:
The 12th I
- Page 192 and 193:
The 12th I
- Page 194 and 195:
The 12th I
- Page 196 and 197:
produce heat and electricity. Fluct
- Page 198 and 199:
The 12th I
- Page 200 and 201:
The 12th I
- Page 202 and 203:
The 12th I
- Page 204 and 205:
The 12th I
- Page 206 and 207:
The 12th I
- Page 208 and 209:
The 12th I
- Page 210 and 211:
To assure that the temperatures mea
- Page 212 and 213:
The 12th I
- Page 214 and 215:
The 12th I
- Page 216 and 217:
The 12th I
- Page 218 and 219:
The 12th I
- Page 220 and 221:
production and provide for marginal
- Page 222 and 223:
The 12th I
- Page 224 and 225:
The 12th I
- Page 226 and 227:
The 12th I
- Page 228 and 229:
The 12th I
- Page 230 and 231:
The 12th I
- Page 232 and 233:
The 12th I
- Page 234 and 235:
The 12th I
- Page 236 and 237:
The 12th I
- Page 238 and 239:
The 12th I
- Page 240 and 241:
The 12th I
- Page 242 and 243:
In addition, it can also be observe
- Page 244 and 245:
The 12th I
- Page 246 and 247:
owner is normally only interested i
- Page 248 and 249:
The 12th I
- Page 250 and 251:
The 12th I
- Page 252 and 253:
The 12th I
- Page 254 and 255:
The 12th I
- Page 256 and 257:
The 12th I
- Page 258 and 259:
The 12th I
- Page 260 and 261:
The 12th I
- Page 262 and 263:
The 12th I
- Page 264 and 265:
The 12th I
- Page 266 and 267:
The 12th I
- Page 268 and 269:
The 12th I
- Page 270 and 271:
The 12th I
- Page 272 and 273:
The 12th I
- Page 274 and 275:
The 12th I
- Page 276 and 277:
The 12th I
- Page 278 and 279:
The 12th I
- Page 280 and 281:
The 12th I
- Page 282 and 283:
The 12th I
- Page 284 and 285:
The 12th I
- Page 286 and 287:
The 12th I
- Page 288 and 289:
The 12th I
- Page 290 and 291:
Stockholm district heating system a
- Page 292 and 293:
The 12th I
- Page 294 and 295:
The 12th I
- Page 296 and 297:
The 12th I
- Page 298 and 299:
The 12th I
- Page 300 and 301:
The 12th I
- Page 302 and 303:
The 12th I
- Page 304 and 305:
The 12th I
- Page 306 and 307:
The 12th I
- Page 308 and 309:
The 12th I
- Page 310 and 311:
The 12th I
- Page 312 and 313:
The 12th I
- Page 314 and 315:
The values presented do of course l
- Page 316 and 317:
The 12th I
- Page 318 and 319:
The 12th I
- Page 320 and 321:
The 12th I
- Page 322 and 323:
The 12th I
- Page 324 and 325:
The 12th I
- Page 326:
The 12th I