SPEED CONTROL OF THE HP"ZEMLIANE"
MAIN NETWORK PUMPS
SUMMARY
The ongoing implementation of new automatic heating substantions in the apartments
houses and installation of regulating valves on the individual room radiators
cause substantial variations of the domestic heat consumption.
The aim of the case study is to increase efficiency of the HP "Zemliane",
through saving electrical energy, consumed by the main heating network pumps,
regulating their flows, respectively heating energy, by variable speed converters
(VSC).
The case study was financed by the Sofia Municipality as part of the Municipality
share for founding SOFENA under the SAVE II project in 2001.
In the development of the project experts from HP "Zemliane" and two
professors form Technical University of Sofia took part.
Context
The City of Sofia has 4 District Heating Regions with own District Heating Plants.
One of the biggest is the "Zemliane" Heating Plant (HP). The Plant
is 51% Municipality owned and 49% State owned. Because of the continually growing
prices of the natural gas, it is crucial for the HP to increase its efficiency,
allowing decreasing of the losses in the plant and hence maintain the prices
of the heating energy for the households in reasonable limits. Otherwise, some
of the consumers should be forced to decline using the district heating. On
the other hand, the ongoing implementation of new automatic heating substantions
in the apartments houses (in Bulgaria, over 95% of the flats are private properties)
and installation of regulating valves on the individual room radiators, substantial
variations of the heat consumption occur. This forced initiation in 2002 of
a project, assigned to SOFENA, for control the delivery of the heating energy
by controlling the flow of the heating water.
Objectives
The aim of the project is to increase efficiency of the HP "Zemliane",
through saving electrical energy, consumed by the main heating network pumps,
regulating their flows, respectively heating energy, by variable speed converters
(VSC). Up to now, the flow rates were regulated by means of throttling valves
at the output of the pumps. This results in great losses of electrical energy,
consumed by the pumps. The ultimate result of the project was development of
Technical Specification for VSC purchase bid invitation.
Process
The project has two phases:
- Investigation of the hydraulic and temperature processes;
- Choice of means to effectively regulate the speed of the main network pumps.
In the first phase, the investigations were held using software modeling of
the heat distribution network and the HP itself. A number of typical scenarios
were simulated using real data for the outdoor temperature and the variability
of the hourly heat consumption due to concrete needs of the inhabitants. Thus,
the expected variations of the heat loads were determined and the necessary
variations of the heating water flows (and temperatures) are examined. The investigations
took into consideration the comfort of the consumers too. Based on the software
simulations, the number of pumps and the structural scheme for installation
of the VSCs was developed. The VSCs were chosen because they represent the most
efficient method for speed regulation of the AC motors of the pumps. Again a
simulation of the heating region with the VSCs was performed to verify the concept
adopted. The expected savings of electrical energy and the investments Rate
of Return were calculated.
In the second phase, a comprehensive specification
of the requirements for the envisaged VSCs, appropriate for the existing pump
motors, was presented. The necessary measuring devices and controllers for development
of an overall control system were specified too.
There were no considerable problems.
Financial resources and partners
The project was financed with 10 kEURO by the Sofia Municipality
(through it's firm "Toploficatzia-Sofia"Plc.) as part of the Municipality
share for founding SOFENA under the SAVE II project in 2001.
In the development of the project experts from "Toploficatzia-Sofia"Plc.,
HP "Zemliane" and two professors form Technical University of Sofia
took part.
Results
For the purpose of the model evaluation, the following table presents a comparison
of the total heating water flow and the heat energy consumption values from
real measurements, without pumps speed regulation, and those calculated by the
model, with pumps speed regulation. During the real measurements, the hot water
flow was regulated by throttling valves.
As could be seen, the coincidence of the flow values
from the real measurements and the model is very close, but the modeled values
of the heating energy is overestimated by the model for hot winter and summer
days. The model values for the heating energy are greater because during the
simulation experiments we tried to meet as close as possible the requirements
for the consumers' comfort.
Note: The heating energy during summer is for domestic hot water
only.
The next table presents a comparison between pumps' electricity consumption without speed regulation (100%) and with speed regulation. Further, the expected savings are calculated. As could be seen, considerable savings are expected, especially during summer days.
From statistics we have the following figures for the
number of the three types of days:
· Cold winter days 41,
· Hot winter days 124,
· Summer days 200.
The expected savings due to the pumps' regulation are:
For the cold winter days: 41days õ 17,907 ÌWh = 734,187 MWh,
For the hot winter day: 124 days õ 32,049 ÌWh = 3 974,076 MWh,
For the summer days: 200 days õ 34,307 ÌWh = 6 861,400 MWh,
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Total: 11 569,663 MWh
Lessons learned and repeatability
It is beyond any doubt that all heat plants need regulation
of the heating water flow to decrease their own energy losses. The most efficient
method, known so far, for regulation the flow of pump with an AC motor is by
means of Variable Speed Converter. Irrespectively from the exact value of the
investment rate of return, our opinion is that all heating plants in Bulgaria
and those using CHP technology should be equipped with VSCs. Therefore, we consider
the project as having a high potential for replicability.