RVH/BCH Data Centres Proposals for Surge Protection and Ventilation

Transcription

1 REPORT Proposals for Surge Protection and Ventilation BELFAST HEALTH AND SOCIAL CARE TRUST ROYAL GROUP OF HOSPITALS GROSVENOR ROAD BELFAST BT12 6BA Rev. 01 6th September 2013

2 Table of Contents 1.0 Ventilation Installations. 2.0 Electrical Installations.

3 1.0 Ventilation Installations. 1.1 Introduction During the recent thunderstorms experienced in the region, the power to the Data Rooms at both the RVH and BCH Data Centre s had several high frequency voltage transients superimposed on it by ground lightning strikes or NIE auto recloses on the mains. The Computer Room Air Conditioning Units (CRAC) Units are supplied directly from either of two generator backed mains supplies. The CRAC Units protection electronics interpreted these transients as symptomatic of critical faults and shut the air-conditioning systems down. Critical faults require a manual reset however before this could be achieved the computer room servers had crashed on over temperature. 1.2 Preferred Option from BHSCT Mechanical Ventilation. The brief received from the BSCHT Estates department is to review the option of providing ventilation fans to alleviate the heat gains when the CRAC units are not initiated. 1.3 Review of Existing Conditions A survey was carried out by IN2 Engineering Design Partnership in both the RVH and BCH Data Centre s to review the feasibility of providing the ventilation fans and associated ductwork distribution systems of which the outcome is further explained herein. The existing CRAC units are down flow units which distribute conditioned air under a raised floor via floor grilles within the aisles between the racks and return to the top of the units. Although the airflow distribution is one of a typical arrangement for Data Centre s of this size, it must be noted that the arrangement of the racks is not typical. It is normal to divide the room into hot and cold aisles with the server s arranged to have all the heat output directed into one aisle ( hot ) and the front of the servers facing into the adjacent aisle ( cold ). With the typical arrangement the supply air should be provided to the cold aisle which allows the cold air to be drawn through the racks to the hot aisle which is then returned to the CRAC units. Currently there are no defined aisle arrangements. This results in hot spots in being experienced in certain areas. Although this is not a major concern when the CRAC units are in operation, it would be of great concern if the units are not in operation as typical Data Centre s require substantial amounts of cooling. It is estimated that the current cooling load for the Centre s would be between 80KW

4 and 100KW. This heat gain would equate to approximately 8.5m³/s of conditioned air being delivered to the rooms. In order to ensure adequate airflow management is maintained, two options are available as follows: 1.4 Option 1: Provision of Unconditioned Ventilation Air Excessive amounts of unconditioned ventilation air would be required to maintain an acceptable level of heat removal from the space (controlling to approximately 40 C). This would equate to an air change rate in the region of 145 Air Changes per Hour. Supply and extract systems would be required due to the volumes anticipated. With the racking arrangements, as previously identified, and with the need for high level supply and extract locations, the air would have to be distributed throughout the Data Centre s in such a manner to ensure there is no poor airflow management which could lead to short circuiting from the cold to the hot aisle and will reduce both the efficiency and the capacity of the proposed ventilation equipment. Diffusers that dump air straight down should be selected and located directly in front of the racks. The Data Centre requires 24 hour cooling, even during colder periods of weather, and with an unconditioned arrangement could lead to exhausting high heat loads onto a rack which can lead to overheating alarms being experienced. Equipment with non-standard exhaust directions must be addressed to achieve a front-toback airflow arrangement. Hot air should be removed immediately as it exits the equipment. Low temperature within the Data Centre could cause great problems if these fans were called for during the winter weather, with some servers possibly shutting down. To compensate for this, the system would require having a recirculation capability which would allow the air to pass through an adiabatic humidifier in order to reclaim return air heat. Although Humidity control is less of an issue with most equipment operating between 10 and 90% RH, the humidity is dependent on the cold aisle supply temperature (set point normally at 18.5 C). There is physically no room for the distribution systems that would be required as well as wall space for filters, fans, humidifiers and louvres (approximately 6-10m² of free area for both intake and discharge louvres).

5 1.5 Option 2: Surge Protection for the Existing CRAC Units The CRAC units have a built in microprocessors giving them full control. It has become apparent that the current CRAC unit control algorithms are the cause of the unit s failure to restart once power is restored. The auto restart function will only activate in the event of a CLEAN Power loss & CLEAN power up. However, should a fault occur with the power supply such as under / over voltage, phase imbalance, loss of one or two phases, then the unit will stop on critical alarm and have to be reset manually. This function cannot be overridden for safety reasons. In light of this then surge protection should be put in place which will protect the equipment and prevent the critical alarms from occurring. 1.6 Proposal As there are too many constraints associated with the provision of mechanical ventilation as secondary back-up it is IN2 Engineering Design Partnerships opinion that the measures to be take in relation to surge protection as outlined within Section 2 of this report shall provide a stable power supply to the units thus allowing them to restart automatically. If the power is interrupted and with the surge protection in place, no fault will be recognised by the CRAC units when the power is restored, thus they will restart automatically. The BMS will always maintain an enable signal to the CRAC units. A further investigation of the controls should be carried out to determine if there are any relays installed within the enabling from the BMS (e.g Fire alarms) which may need to be re-evaluated to ensure a strategy is put in place to enable the CRAC units to restart automatically.

6 2.0 Electrical Installations. Lightning Protection Installation - Surge Protection Measures 2.1 Introduction Any installation intended to provide protection from the effects of lightning shall be required to be in compliance with the recommendations of BS EN Protection against Lightning. Surge protection designed to protect electrical or electronic equipment comprises only one element of a holistic lightning protection system, and is specifically addressed by BS EN Part 4:2011, Protection against Lighting, Electrical and electronic systems within structures. The various elements of an inclusive lightning protection system are shown in the diagram below taken from BS EN :2011 Protection against Lightning, Part 1: General Principles. Lightning protection systems are categorised into four Lightning Protection Levels (LPLs), (I) through (IV), with LPL (I) offering the highest level of protection and LPL (IV) suitable for the lowest risk applications.

7 2.1 Introduction cont d The basic concept of Lightning Protection Zones (LPZ s) and the placement of equipment and associated surge protection devices are indicated schematically on the figure below. The various categories of LPZ are defined in BS EN as below:- LPZ 0A :- Zone where the threat is due to the direct lightning flash and the full lightning electromagnetic field. The internal systems may be subjected to full or partial lightning surge current. LPZ 0B :- Zone protected against direct lightning flashes but where the threat is the full lightning electromagnetic field. The internal systems may be subjected to partial lightning surge currents;

8 2.1 Introduction cont d LPZ 1 :- Zone where the surge current is limited by current sharing and by isolating interfaces and/or SPDs at the boundary. Spatial shielding may attenuate the lightning electromagnetic field; LPZ 2 :- Zone where the surge current may be further limited by current sharing and by isolating interfaces and/or additional SPDs at the boundary. Additional spatial shielding may be used to further attenuate the lightning electromagnetic field. Surge protection relates specifically to limiting transient over-voltages on the consumers electrical installation. Transient over-voltages are short duration, high magnitude voltages peaks, commonly referred to as surges or spikes. The most common source of extreme transient over-voltages are lightning strikes. Lightning strikes, whether direct or indirect can cause significant damage to unprotected systems and structures. In addition to high magnitude spikes caused by lightning, items of electrical and electronic equipment are continually subjected to low magnitude transient overvoltages which are created as a result of switching operations of inductive loads such as Motors or Air Conditioning equipment. Low magnitude transients can also be initiated by short circuit currents being interrupted by tripping of protective devices. While the switching transients are of a lower magnitude than those produced by lightning strikes, they are much more frequent and can cause degradation and eventual failure of electronic equipment susceptible to the levels of over-voltages produced. The provision of an appropriate surge protection installation is essential for any critical electrical or electronic equipment to ensure continued operation and to ensure the expected lifetime of the equipment is protected. In order to protect critical equipment effectively it is critical to establish and maintain a holistic lightning protection system, with Surge Protection Devices located at defined boundaries between LPZ s as indicated above.

9 2.2 Existing Conditions Belfast City Hospital BSO Data Room in Telephone Exchange Basement. Royal Group of Hospitals BSO Data Room in EENT Lower Ground Floor It is our understanding that lightning strikes during recent storms have caused significant problems to the operation of the Air Conditioning Units in the Data Centre. The Air Conditioning units perform a critical function in cooling the space within the Data Centre to acceptable environmental conditions. We understand that the existing Air Conditioning units ceased to function as a result of lightning strikes in the area producing surges on the network. It is our understanding that similar circumstances to those experienced at the Belfast City Hospital site have also impacted the Air Conditioning Units at the Royal Group of Hospitals BSO Data room. We understand that existing Air Conditioning units on the Royal Site also ceased to function as a result of lightning strikes in the area producing surges on the network. In order to provide a comprehensive solution which will mitigate the risk of these events re-occurring, the first point of action is to have the existing lightning protection system inspected and tested by an approved Lightning Protection Specialist installer. Any damage resulting from recent strikes should be repaired as a matter of urgency. This is a direct requirement of BS EN following any strike to a LPS. The inspection should be carried out by a competent specialist Lighting Protection System Installer as a matter of urgency. We would recommend that the Belfast Trust engage J & J Mowbray to carry out the required Test & Inspection of the Lightning Protection System. J & J Mowbray are a recognised and highly regarded specialist in the field of Lighting and Surge Protection Systems in Northern Ireland, and would be competent to carry out the required investigations.

10 2.3 Option 1 - Protection from Surges on Mains Incoming Cables Following the satisfactory inspection and testing of the LPS, additional surge protection should be installed onto the incoming mains supply cables. The existing Main Switchboards serving the respective Data Centres currently have dual supplies, in the form of preferred and alternate supplies. It has not yet been possible to determine where each of the power supplies originate from for the BCH Data Centre, and whether the preferred and alternate supplies are derived from independent transformers. The exact details of the infrastructure cabling will be investigated further and detailed within the design documentation. The supplies for the RGH Data Centre originate from alternate transformers located within the A-Block / EENT sub-station. (T19 & T20) The mains incoming cables present the greatest risk in terms of surges being presented to the Data centre Air Conditioning equipment. In respect of this, the optimum location for a surge protection device would be in parallel with the main incoming cables. As there are two sources of supply, the installation of surge protection devices could be carried out without a shut-down being necessary, as works can be carried out on one cable with the other remaining live. However, there will be an elevated risk of failure during installation works as only one of the preferred or alternate supplies will be available. This means there will be a lower level of protection afforded until the works are complete. If this is an acceptable risk to Belfast Health and Social Care Trust then this would be the optimum solution in relation to protecting the Air Conditioning units, and simultaneously all other devices and equipment served from the Switchboard. A representative schematic of the Option 1 proposal is appended to this report. See Schematic Diagram B1358-SK-E0780_1

11 2.4 Protection from Induced Surges on Outdoor Condenser Units The outdoor units at the City Hospital Data Centre are both wall mounted and ground mounted. The units are located within a narrow courtyard between the Telephone Exchange and the Adjacent Building. The adjacent building is relatively tall in comparison and the area in which the Condenser units are located is enclosed by steel fencing. The outdoor units at the Royal Site are wall mounted at low level in comparison to the height of the Building. A risk assessment would be required to be carried out to assess the level of risk of strike in each area as defined within BS EN It is our estimation that the risk of strike within these areas would be relatively low and additional surge protection to Outdoor Condenser Units may not be required. However this is only an estimation based on the general principles of Lightning risk as set out by BS EN :2011, and should be confirmed by a formal risk assessment carried out by a specialist Lighting Protection System Installer. We are familiar with J & J Mowbray Ltd who are recognised specialists in this field and are the authorised supplier and installer of Furse surge protection equipment for Northern Ireland. We would recommend that the Belfast Trust engage J & J Mowbray to carry out a formal risk assessment to determine the associated level of risk. If it is determined that additional surge protection is required for the outdoor condenser units, this will increase the disruption and cost of the project as each Condenser unit will require an independent SPD connected in-line which will need to be located at the isolator for each individual unit. Each SPD will be required to be fitted within an IP Rated enclosure should this be required. 2.5 Option 2 - Protection from Surges on AC Unit Sub-mains Cables As previously highlighted in section 2.3, the optimum location for surge protection devices would be directly onto the incoming sub-mains supply cables. However, if it is operationally not possible to facilitate these works, a second option would be to provide surge protective devices in-line with the Air Conditioning Units. This installation would only serve to protect the AC units and would not offer protection to the entire installation. This option should only be explored if option 1 is not possible. A representative schematic of the Option 2 proposal is appended to this report. See Schematic Diagram B1358-SK-E0780_2