Pilot #1: Pont Saint Martin DC

Table 5.1 lists the main characteristics of DC sub-systems models that are used to assess the thermal and electrical energy flexibility in the PSM case.

Table 5.1. PSM DC Characteristics

Sub-System Characteristics

Cooling Sub-System Coefficient of Performance 𝐶𝑂𝑃 = 1.6

Maximum Cooling Capacity 𝑀𝐴𝑋𝐶𝑜𝑜𝑙𝑖𝑛𝑔= 460 𝑘𝑊ℎ

IT Severs Maximum Power Consumption 𝑀𝐴𝑋𝐼𝑇= 720 𝑘𝑊ℎ

Delay Tolerant Workload Percentage = 20% UPS and Electrical Storage

System

Maximum Charge Rate 𝑀𝐴𝑋𝑅−𝐸𝑆𝐷= 450 𝑘𝑊ℎ

Maximum Discharge Rate 𝑀𝐴𝑋𝐷−𝐸𝑆𝐷 = 1300 𝑘𝑊ℎ,

Maximum Storage Capacity 𝑀𝐴𝑋𝑆−𝐸𝑆𝐷 = 450 𝑘𝑊ℎ

Diesel Generator Maximum Generation Capacity 𝑀𝐴𝑋𝐷𝑖𝑒𝑠𝑒𝑙= 3600 𝑘𝑊ℎ

Table 5.2 presents the electrical energy flexibility available in this DC case.

Table 5.2. PSM DC Electrical Flexibility Mechanisms

Sub-System Electrical Flexibility Mechanism Minimum Reaction Time Minimum Response Duration Maximum Response Duration Observation

IT Servers Shift Delay Tolerant

Workload 1 hour 1 hour Until workload deadline Depends percentage of delay on tolerant workload considered

UPS and

Electrical Storage System

Power Totally DC Instant A few seconds 20 minutes up to 1 hour Power Partially of DC

(50% - either branch A or branch B)

Instant A few seconds 20 minutes up to 1 hour Air Cooling Sub-

System Power off refrigerant unit to save energy Instant A few seconds 10 minutes Can take place only once every day Diesel

Generator Power Totally the DC 50 seconds A few minutes 4 days

Thefirst option of electrical energy flexibility is considered to be enacted by shifting the delay tolerant workload in time. In this case the DC (see Figure 9) can decrease its energy consumption over the response period with about 220 kWh, corresponding to the energy consumed by the servers and the cooling sub-

system energy consumption. Furthermore, by shifting the load to a different period, the DC can increase the energy consumption with up to 220 kW, until the maximum resource usage is achieved.

Figure 9. Electrical energy flexibility potential as result of shifting delay tolerant workload

Thesecond option was using the UPS and batteries systems as a source of flexibility by cutting out the DC from the grid and using them for powering the DC. By using the UPS system, the DC can reduce its energy consumption up to 0 kWh over a period of 20 minutes (interval 1-2.5 see Figure 10). Then, the batteries have to be recharged, so the DC increases its energy consumption over a period of approximately one hour to recharge the batteries (interval 2.5 – 6 in Figure 10). The DC increases its energy demand by 600KWh while charging the batteries.

Figure 10. UPS and batteries electrical energy flexibility

The third option was considered to be using the cooling sub-system as a source of electrical energy flexibility by powering off cooling sub-system refrigerator to decrease the DC overall energy demand. In this DC the

three refrigerant units, each consuming 100 kWh can be turned off and the cooling sub-system leverages on the cold water from the hydraulic manifolds to cool the servers. This mechanism decreases the cooling power consumption by about 300 KW, thus over a period of 10 minutes about 50 kWh are saved. Figure 11 shows the power consumption of Refrigerant Unit GF1 during such a test scenario.

Figure 11. Power consumption of refrigerating unit GF1

To bring the system back to steady state, the refrigerant unit increases its power consumption up to 140 KW in the next hour. The DC increases its energy consumption with 60 kWh.

Figure 12. Using the cooling sub-system refrigerator units as source of energy flexibility

Thefourth option was considered to be using the diesel generator as source of energy flexibility. In this case the DC can reduce its energy consumption from the grid to 0 kWh, by powering all its infrastructure with the energy produced by the diesel generator. During the diesel generator start-up time (20 seconds startup and

30 seconds sync time), the DC energy demand is supported by the UPS system batteries, then it can be supported by the diesel generator for long periods, up to 4 days.

Table 5.3 presents a summary of the flexibility potential of the PSM DC, illustrating the lower and upper bounds with respect to the DC baseline for each flexibility mechanism identified.

Table 5.3. PSM DC electrical energy flexibility summary

Flexibility Mechanism Minimum Bound (below

baseline) Maximum Bound (above baseline)

Flexibility

Duration Flexibility Load Flexibility Duration Flexibility Load

Shift Delay Tolerant Workload 1 hour 220 kWh 1 hour 220 kWh

UPS Charge/Discharge Totally 20 minutes 400 kWh 1 hour 600 kWh

UPS Charge/Discharge Partially 40 minutes 400 kWh 1 hour 600 kWh

Power Off Cooling Sub-System Refrigerator Units to

Reduce Energy Consumption 10 minutes 50 kWh 1 hour 60 kWh

Diesel Generator up to 4 days 1100 kWh - -

To determine the potential thermal flexibility and heat reuse we considered and simulated a heat reuse system based on a heat pump with the following characteristics: energy consumption of compressor 200kWh, 𝐶𝑂𝑃𝑐𝑜𝑜𝑙𝑖𝑛𝑔 of 3.8 and 𝐶𝑂𝑃ℎ𝑒𝑎𝑡𝑖𝑛𝑔 of 2.3. Using this heat pump model, the DC heat generation

baseline is closely related to the workload. For the workload consuming 720 kWh of electrical energy, an amount of 246 kWh of heat can be generated.

We considered and investigated the potential of two thermal flexibility mechanisms that allow the DC to increase or decrease its heat generation (see Table 5.4).

Table 5.4. PSM DC thermal flexibility mechanisms considered

Sub-system Thermal Flexibility Mechanism Minimum Reaction Time Minimum Response Duration Maximum Response Duration Observation IT Servers and

Server Room Shift delay tolerant Workload 1 hour 1 hour Until workload deadline

Depends on the percentage of delay tolerant workload Air Cooling Sub-

System Post cooling of server room by powering off refrigerant unit Few seconds Few seconds 10 minutes Can take place only once every day By shifting delay tolerant workload to improve the thermal energy flexibility response of the server room, the DC can decrease or increase its heat generation with up to 50 kWh with respect to the baseline, as shown in Figure 13.

Figure 13. PSM DC heat generation flexibility by using the delay tolerant workload time shifting

The refrigerant units, each consuming 100 kWh can be turned off and the cooling sub-system leverages on the cold water from the hydraulic manifolds to cool the servers. Thus, over a period of 10 minutes, both the temperature of hydraulic manifold output water (to bunkers) and the temperature of hydraulic manifold input water (from bunkers) increased as shown in Figure 14, from 8 °C, respectively 10 °C up to 14 °C, and 16 °C, for the output and input manifolds.

Figure 14. Water temperatures at the hydraulic manifold

After 10 minutes, the refrigerant units are restarted and the water is cooled back to normal operating temperature over a period of 50 minutes, to reach the steady operating conditions of 8°C for the hydraulic manifold output water and 10°C for hydraulic manifold input water. During the period when the refrigerant units are switched off, the heat generation drops down to 0, while during the transient state of 50 minutes to steady state, an amount of extra 40 kWh of heat is generated, as shown in Figure 15.

Figure 15. Using the cooling sub-system refrigerator units for heat flexibility

The following table presents a summary of the thermal flexibility potential of the PSM DC, illustrating the lower and upper bounds with respect to the DC baseline for each flexibility mechanism identified.

Table 5.5. PSM DC Thermal Flexibility Summary

Flexibility Mechanism Minimum Bound (below

baseline) Maximum Bound (above baseline)

Flexibility

Duration Flexibility Load Flexibility Duration Flexibility Load

Time shift of delay tolerant workload 1 hour 50 kWh 1 hour 50 kWh

Post cooling using the cooling sub-system

refrigerator units 10 minutes 0 kWh 50 minutes 40 kWh