Alpine Energy Offices

The Challenge

Alpine Energy, the electricity retailer in the South Canterbury area were looking to upgrade from their existing offices, to a new, purpose built facility, which would accommodate both their operation, and that of an associated organisation, Netcon. A multi-winged two level facility was originally proposed, and an initial design presented to the client. The initial design was not progressed, and an alternative design-build proposal from Thompson Engineering adopted instead.

This design has approximately the same floor area, 3000 m2 over two levels, but with a much-simplified form. The internal spaces are almost entirely open plan, with only meeting rooms, training rooms and the network control operations segregated off from the other spaces. No 2 Alpine Energy HVAC Design

Thompson engineering engaged Bryn Martin Limited to provide the engineering of the mechanical services systems, and to provide a peer review of the hydraulic services. As an electricity retailer, Alpine energy wished to be seen as a responsible business by minimising inefficiency in providing their buildings heating, cooling and ventilation, but at the same time, need to be fully operational 24 hours a day, for their electricity network control functions.

Main Features

Direct expansion air conditioning units driven by heat recovery type (simultaneous heating and cooling) condenser units.
An energy efficient means of tempering the incoming ventilation air.
Load sensing capacity control for all air conditioning and ventilation systems.
Systems which will deliver the required heating, cooling and ventilation regardless of outside
conditions, from -5°C to 30°C.

The Response

In order to asses the peak demands for cooling, heating, and outdoor air ventilation, the building was modelled in the Carrier E20 thermal modelling package. The main open plan areas of each floor (3 on the ground floor and 4 on the first floor) were divided into perimeter and interior zones and modelled accordingly. To these were added the individual meeting rooms and other partitioned off spaces. The ventilation loads determined by the model were compared with those determined from the estimated occupancies and adjusted as necessary. The modelling outputs were used to size the outdoor condensing units and to determine the minimum capacities of indoor units that needed to be specified for the various areas of the building.

The modelled heating and cooling capacities were used in conjunction with assessments of the necessary air flows to adequately condition each zone within the building to determine the size and quantity of air

conditioning units that would be needed to serve each zone. The assessed ventilation flows were used to size air handling systems needed to supply the outdoor air.

With the general sizes of the plant determined, the specific types of equipment were chosen. In this case, ceiling cassette type AC units were assessed to be the most cost-effective way of delivering the required level of comfort, while minimising the installation of ductwork and grilles in the ceilings.

For the ventilation system, air handlers (AHUs) were chosen with direct expansion coil heating banks driven by variable capacity outdoor condenser units were chosen, to provide adjustable levels of tempering to the incoming air, to meet the demand at the time.

In addition to the AHUs, air to air heat recovery units were placed up stream of the AHUs, to transfer heat from the air being exhausted to the incoming air, thereby reducing the need for tempering of the incoming air. Air handlers generally have two heat exchanger units supplying them, with one carrying the exhaust air from the WC and shower areas, and the other carrying the air returned from the general office spaces.

The Works

The equipment delivered for this project consists of 5 Mitsubishi Electric City Multi R2 VRF air conditioning systems of various capacities, driving compact and standard size ceiling cassette units. The system was initially split into 4 systems, serving each end of the ground and first floors. One system was further divided to provide a system with a small enough refrigerant charge to supply the smallest rooms in the building.

The ventilation systems are similarly split into 4 units, with EPI Clever AUHs serving the same sections of the building indicated above. Each AHU has a pair of inverter driven Mitsubishi Electric AHU condenser units driving its heating coils and two Air-Change heat recovery units up stream of it pre-treating the incoming air. Capacity control is driven in response to CO2 sensors that are located in the office area return air ducts.

All of t No 4 Alpine Energy HVAC Design he mechanical services equipment is controlled from a single AE-200 central control unit, with appropriate additional modules to provide on off control of AHUs and heat recovery units.

All of the AC and ventilation system condenser units are located at ground level, adjacent to the building, to make maintenance safer and easier.

In addition to the design of the mechanical services, Bryn Martin also provided the design of the seismic restraints for the air conditioning systems, air handlers and ductwork, as well as for the plumbing and drainage systems.

For more Information on this or any other project or service please contact Brian Anderson or Tim Allan.

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