This report is written as part of the final exam at the education as Bachelor of Technology Management and Marine Engineering. The report is written subsequent to an internship at the heat distributing company, Ikast Værkerne A.m.b.A.
The subject of the report is how to dimension a new district heating system at the end of a distribution line. Two methods are evaluated: boosting pump and an increasing of the size of the heating pipes. This is a current issue at Ikast Værkerne, since they are about to expand their heating system to new residential areas at one end of their distribution system. Hence, Ikast Værkerne is used as case in this report, why calculations and results are based upon these new residential areas in the city of Ikast.
The areas are supplied from a pipe that has enough capacity at the moment. But as the areas become fully settled, the demand of heat will cause a flow of water so high that the pressure drop in the supply pipe will result in a negative differential pressure. This means that the necessary amount of heat cannot be delivered without either adding a boosting pump in the return pipe or increasing the size of the pipe.
The option of upgrading the current size of the pipe is rejected. The rejection is based on that the present distribution pipe is established in 2010, and the option of putting down a parallel pipe will cause too much disturbance for the citizens. Therefore, the only possible solution is to add a boosting pump to the system.
In the selection of a boosting pump you need to consider two alternatives. The pump can either be selected with a head that can compensate for the largest pressure drop in the current piping system plus a differential pressure of 0,5 bar. Alternatively you can choose a pump with a head that compensates for a pressure drop so high that the resulting pressure at the inlet of the pump is 0,5 bar plus a differential pressure of 0,5 at the end of the line. The choice of the second solution means that you can use smaller pipes. This can happen because of the possibility of increasing the pressure drop by downsizing the pipes.
The result of the analysis of the two ways of dimensioning with a boosting pump is that the one with the largest head in general implies savings on the cost of establishing the piping system. The pump is a bit more expensive and a few more reductions are needed, but the use of smaller pipes means significant savings.
The running costs of the second method are twice the price of the first. Savings on the heat loss of the pipe systems though compensates some of the extra cost of running the pump. The lower heat loss partly occurs because of the smaller surface of the pipes, partly because of the higher velocity of the water.
The final conclusion of the report is that the second boosting pump method is the advisable choice from an economical perspective. Furthermore, there are advantages in the daily use from this choice. These are higher temperature at the end of the line, and the possibility of sustaining a reasonable velocity of the water, if the heat requirement should end up lower because some of the houses choses individual heating pumps.