Consideration on climate energy efficiency impact.

Jiga, Gabriel ; Grigoriu, Mircea ; Ciuca, Ion 等

1. INTRODUCTION

The proposed controlled operation system, which is compared with the actual operation systems with three ways vane proposed system has the main advantage the adjustment in the same time both circulation flow and pump speed system.

Its simple schema is presented in fig. 1. It coordinates the operation of circulator pump and control valve. Depending on the control signal issued by the higher-level heating controller, the two control valves adjust the resulting volume flow rate pumped through the consumer installations (Dimonie et al 2007), (Dragoi et al., 2007).

The supply temperature is increased by the higher-level controller. This results in hydraulic savings regarding both volume flow rate [DELTA]Q and discharge head AH, whose product is proportional to the corresponding electrical power savings for the circulator pump, considering electrical power equation

[P.sub.el] = K + Q(t) x H(t) x dt (1)

where:

[P.sub.el]--electrical necessary power,

K--constant which describes the efficiency of circulator pump and frequency inverter as well as water density and acceleration due to gravity,

Q(t)--flow-time characteristic,

H(t)--Heat-time characteristic.

[FIGURE 1 OMITTED]

Thermal output of the heating circuit is calculated for the design point as the product of volume flow rate Q and temperature [DELTA]T.

[P.sub.th] = 1.163 x Q x [DELTA]T (2)

where:

[P.sub.th]--thermal power output.

The innovative control concept consists in regulating thermal output by variation of the temperature differential and the volume flow rate, considerably reducing the water volume to be pumped through the heating circuit.

The radiator diagram illustrates that volume flow rate can be reduced while thermal output at the consumer installations stays the same, if the supply temperature is increased accordingly.

[Q.sub.total] = [Q.sub.2m] + [Q.sub.ls] (3)

where:

[Q.sub.total]--volume flow rate of the radiator,

[Q.sub.2m]--volume flow rate from mixing pipe,

[Q.sub.ls]--volume flow rate from water supplier.

The controller's heating curve is shifted parallel by a fixed amount towards higher supply temperatures. The controller adds the fixed amount [DELTA]T to the supply temperature set point (parallel shift of the heating curve). Due to the increased temperature differential, the nominal volume flow rate is reduced by 25% in all cases, resulting in a new design point for the circulator pump (Grigoriu, 2005).

System valve authority is constant over the entire operating range. This correlation is reflected in the system control curve and explains why the system control curve runs parallel to the system curve.

Depending on the external temperature, the operating point of the system controlled circulator pump moves along the system control curve. As external temperature rises, the operating point moves towards lower volume flow rates and lower discharge heads (Grigoriu, 2006).

Under the influence of external heat load, the operating point also moves along the characteristic curve of the differential pressure controlled pump. Depending on the pump curve set, the discharge head either remains constant ([DELTA]p = constant) or decreases with decreasing volume flow rate ([DELTA]p = variable). All the familiar features of the variable-speed pump and the thermostatic valves are retained.

The differential pressure at nominal load:

[DELTA][p.sub.n] = c x [Q.sup.2.sub.n] (4)

Under part-load conditions, the differential pressure at the balancing valve is reduced as follows (Differential pressure at partial load):

[DELTA][p.sub.t] = c x [(F[Q.sub.n]).sup.2] (5)

where:

F--factor describing the partial load level (0-100)%.

It results the differential pressures at nominal and partial load for branch circuits:

[DELTA][p.sub.t] = [F.sup.2] x [DELTA][p.sub.n] (6)

Therefore, the ratios of the differential pressures are:

[DELTA][p.sub.ti]/[DELTA][p.sub.tj] = [DELTA][p.sub.ni]/[DELTA][p.sub.nj] (7)

If parallel shift of the heating curve is planned, new system will always reduce the volume flow rate for the design point by 25%, based on the volume flow rate the system designer has calculated for a conventional mixing or injection-type system.

The system has to be configured prior to commissioning. This is done by entering the value of the volume flow rate determined for a conventional mixing or injection-type system into the commissioning software, together with the nominal system diameter of the system (parameterization). The system automatically determines the circulator's discharge head required for the design point. To do so, the circulator pump is started up with its minimum discharge head. A corresponding volume flow rate is produced in the heating circuit, which is measured by the system controlled valve at the main feed manifold.

2. ESTIMATED ECONOMIC EFFECTS FOR A SPECIFIC EXAMPLE

The following analysis shows that for a specific case of heating system, it is selected a circulation centrifugal pump, which is controlled on one hand by the proposed control system and on the other hand by a conventional system. The pipe curve of the heating circuit is calculated as the quotient of the pump head (H) and the square of the volume flow rate (Q) (BOA-Systronic, 2008):

[k.sub.heating] = H/[Q.sup.2] (8)

[k.sub.heating]--pipe curve of the heating circuit constant.

The volume flow rate for the design point of the conventionally equipped main feed circuit is

[Q.sub.nc] = 13[m.sup.3]/h. (9)

At this volume flow rate, the pump can provide a maximum head of approximate H=8m. For this case, the following system constant is calculated for the heating circuit:

[k.sub.heating] = 8/[13.sup.2] = 0.0473 (10)

The example is based on a temperature differential of [DELTA]T = 20 K, and the heating curve of the higher-level controller was shifted by 3.5K (parallel shift), resulting a reduction of 25% of the volume flow rate in the design point.

[Q.sub.n] = 0.75 x [Q.sub.nc] = 0.75 x 13 = 9.75 [m.sup.3]/h (11)

[H.sub.n] = [k.sub.heating] x [Q.sup.2.sub.n] = 0.0473 x 9.75 = 4.5m (12)

This new design point Q/H [right arrow] 9.75[m.sup.3]/s / 4.5m can be handled by a smaller selected pump. For the present example, investment costs for the circulator pump are reduced.

The external temperatures measured were plotted for the period mentioned. The diagram shows an average external temperature of approx. 10[degrees]C in the period monitored. Depending on the location, the heating circuits are selected for an external temperature of approx. -12[degrees]C to -15[degrees]C. Regulations stipulate that the building must be heated until the external temperature reaches approx. 16[degrees]C. The temperature difference between the design point and the switch-off temperature of the heating system is [(-12[degrees]C) - (+16[degrees]C)] = 28[degrees]C. The temperature difference between the design point and the average temperature is [(-12[degrees]C) - (+10[degrees]C)] = 22[degrees]C. The ratio between both values is 22/28 = 0.79. This means that in the monitored period both heating circuits on average only require about 21% of the thermal output they were selected for.

3. SOME ELEMENTS OF CONSTRUCTIVE CALCULUS

The mean values of the volume flow rates measured in the two heating circuits are calculated:

Controlling system Flow rate (m3/h) Ratio(Qsn/Qn)
3-way configuration Q n = 11.2 0.29
New System Q sn = 3.2

With the new system, the pump is operated on average at only about 66% of the nominal discharge head at design point:

Controlling system Differential pressure (H) Ratio
3-way configuration H n = 4.4 0.66
New System H sn = 2.9

The pump input power, and thus its power consumption, is proportional to the product of the discharge head and volume flow rate.

The new system operates the pump at reduced volume flow rates and discharge heads. The pump draws much less power from the electricity grid. The new system was shown to save approx. 70% in electrical energy:

Controlling system Input power (W) Ratio
3-way configuration P n = 561 0.33
New System P sn = 184

4. CONCLUSIONS

The most important ecologic effect of the energy efficiency application is the greenhouse gasses mitigation, reducing the electrical energy consumption and, by consequence production. Burning fossil fuels produces C[O.sub.2] emissions of roughly 0.53 kg per 1 kWh of electrical energy produced. Thanks to the drastic reduction in power consumption, the new system therefore makes a positive contribution to environmental protection.

5. REFERENCES

Dimonie, D., Radovici, C., Serban, S., Taranu, A., Vasilievici, V. (2007), Biodegradable compounds from regenerable resources for packings, Mat. Plast., Vol.44, No.2, p.148-155

Dragoi, G., Funar, St., Solea, M., Cotet, C.E. (2007), Simulation and optimization of a waste processing flux, Mat. Plast., Vol.44, No.1, p.77-81

Grigoriu, M. (2005), Pumps and Pumping Installations, Ed. Printech, Bucharest

Grigoriu, M. (2006), Remote Pumped-Storage, Back to Back Variable Speed Operated, WEAC, Session A9- 340-344, Polito, Italy

*** BOA-Systronic (2008). Systematic Savings on Energy and Costs, KSB Know-How series, Germany