A winning case – trigeneration delivers for Dublin law firm

A trigeneration scheme supplies heat, power, cooling and substantial energy cost savings to a Dublin city centre office block. This proves that, where all three energy loads exist, on-site energy generation can be successful in the commercial building sector. The host company buys energy from the plant under a long-term discounted energy supply contract. Brendan Marren reports.

Dublin-based Irish company, Combined Energy Solutions (CESenergy) is looking to change the way city centre businesses think about their energy requirements. In doing so, CESenergy is taking Irish business into the future in environmental terms.

The benefits of CHP and trigeneration are well documented. However, their energy saving systems not only perform well for industry, manufacturing and high consumption businesses, such as large hotel operations, but can also deliver substantial results for large commercial offices. CESenergy is keen to educate businesses with large offices based in Ireland’s commercial centres to convert to better energy systems such as CHP and trigeneration.

A&L Goodbody, one of Ireland’s biggest law firms, is achieving energy efficiency and cutting energy bills by using trigeneration
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A&L Goodbody is one of Ireland’s largest law firms, with 63 partners and 215 legal staff. As one of Ireland’s top law firms, the company has an international outlook, having advised many international companies on successful investments in Ireland, and the firm regularly partners some of the world’s leading international law firms on the Irish aspects of multi-national business transactions. A&L Goodbody’s Irish headquarters building is a 10,000 m2, five-storey purpose-built office block in Dublin’s highly developed International Financial Services Centre (IFSC).

Prior to the installation of the trigeneration system, the building’s heating and electricity requirements were provided by two main sources – natural gas-powered boilers and the national electricity grid. A&L Goodbody’s bills for natural gas and national grid-sourced electricity were costing the company a substantial €600,000 annually.

The law firm’s building had electrical demand, and predictable heat and cooling demand, right throughout the year, so a trigeneration solution was ideal for ensuring year round use of heat from the CHP unit. The CHP unit installed was oversized to allow district heating connection, as well as excess electricity being spilled to the grid.

Figure 1. Annual energy consumption profile – office block scenario
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On average, the plant’s annual heat utilization is over 90%. A&L Goodbody took the decision to outsource operation of the entire energy centre to CESenergy which owns and operates it on an Energy Supply Contract (ESCo) arrangement.


A&L Goodbody’s decision to commission CESenergy was motivated by a number of factors, one of which was the significant financial savings that a trigeneration unit could deliver. It was estimated that, in terms of direct energy costs alone, the law firm stood to make savings in the region of €40,000 each year.

In addition, it would have had to invest a capital cost of €250,000 for new back-up generators that would otherwise have been needed, plus charges of about €4000 each year for maintenance costs relating to those generators. The environmental benefit delivered by CHP technology, in terms of hugely reduced CO2 emissions, was also a consideration in A&L Goodbody’s decision-making process, being very much in line with the firm’s policy of supporting environmentally sustainable technologies.

A&L Goodbody’s decision to employ an ESCo to take over all responsibilities related to the design, funding, build, operation and maintenance of the reconfigured CHP plant was prompted by the range of benefits that such a move would deliver. In normal circumstances, the capital cost of such a trigeneration CHP plant would be about €1,300,000.

However, because A&L Goodbody opted to enter into a discounted ESCo, the unit is both owned and maintained by CESenergy. The law firm now pays CESenergy a single fee of over €550,000 each year which covers energy procurement, monitoring and maintenance charges, insurance costs etc.


The trigeneration plant installed at A&L Goodbody includes:

  • 1 MW CHP unit
  • 1 MW heat exchanger
  • 445 kW absorption chiller
  • 1.2 MW blast cooler
  • 1.1 MW cooling tower
  • control system
  • thermal meters
  • import/export meter
  • distribution system
  • water treatment
  • lubrication system with supplementary oil tank and automatic top-up
  • automatic starter system with batteries and charger
  • anti-vibration mounts supporting engine/generator monoblock
  • full interface with remote monitoring system.

The Jenbacher engine unit for the A&L Goodbody building
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The CHP unit installed at the A&L Goodbody site uses a GE Jenbacher gas engine unit type JES 320 (see Table 1).

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The York absorption chiller runs on exhaust heat from the engine
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The absorption chiller installed on site is a York Model YIA3B2. It is a single phase type, with a single pass through the condenser and generator (see Table 2 for more details).

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For most of the year, the trigeneration plant at A&L Goodbody operates on thermal load follow, providing the building with all its heat and cooling requirements. At times, thermal load follow results in the production of electricity above that required by the building. In this case, the excess electricity produced by the CHP plant is spilled to the National Grid.

For example, at 12.00 noon, the CHP electrical output is 560.1 kW, the building power requirement is 442.4 kW and therefore 117.7 kW is spilled to the grid. When the plant is operating according to the thermal load, 100% of the heat produced by the CHP is being fed into either the absorption chiller or the heat exchanger and, therefore, the blast cooler is not operational.

In terms of operating the trigeneration plant at 17.30 during a winter month, in the Irish market, there is a peak demand charge between 17.00 and 19.00 of €0.2999/kWh. It is therefore commercially viable to operate the CHP at 100% in this period, spilling excess electricity generated to the National Grid. Another example shows a CHP instantaneous output of 1015.4 kW at 100% operation. The power requirement of the building is 393.6 kW, therefore 621.8 kW of electricity is spilled to the National Grid.

At 100% operation, hot water flows into the absorption chiller, which produces chilled water at a flow and return temperature of 10.2à‚°C and 11.4à‚°C respectively. Water returns from the absorption chiller at 85à‚°C and mixes with the hot water flow to produce water at 90à‚°C, which flows into the heat exchanger.

Any heat above the building’s hot water requirements is sent to the blast cooler. This maintains the return flow temperature below the maximum return limit set point of 72à‚°C. When the plant is at 100% operation, the blast cooler operates at 42.8% because of the excess heat being generated.


Figure 2 illustrates heat and cooling usage at the A&L Goodbody site over a six-month period, incorporating both summer and winter periods. There is a base electrical load of approximately 450 kW throughout the year.

Figure 2. Heat and cooling usage at A&L Goodbody’s site over six months
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During the summer, the heat exchanger load drops to a value as low as 48 kW, while the cooling demand increases to a maximum of 396 kW. This cooling demand requires a heat input of 600 kW from the CHP to the absorption chiller. During the winter, the cooling requirement of the building drops to a value as low as 120 kW, which requires a heat input of 280 kW from the CHP. The heating demand of the building increases to 360 kW. The increase in the heat dump can be attributed to the running of the CHP at 100% during the peak charge period of 17.00-19.00.

The efficiency of the trigeneration plant is maximized throughout the year through the ability of the plant to alternate CHP heat usage between the absorption chiller and heat exchanger in the summer and winter months respectively.

Figure 3. Trigeneration plant efficiency over a six month (winter-summer) cycle
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This is illustrated in Figure 3 which shows a relatively small amount of heat being dumped for a large part of the six month period. The increase in the heat dump during the winter months can be attributed to the increase in heat generated when the CHP is running at 100% during the peak hours of 5pm and 7pm.


The benefits of this trigeneration solution to A&L Goodbody as it currently stands include:

  • reduced electrical, chilling and heating energy costs
  • enhanced client environmental and energy efficiency footprint
  • no capital expenditure on energy centre plant
  • security of supply – primary source of electricity; can also be used as back up
  • eliminates maintenance costs.


As stated, this CHP unit is set up on an ESCo basis, whereby CESenergy has taken over full responsibility of the entire energy bills for A&L Goodbody. The law firm therefore receives a single bill from CESenergy for all its electrical power, chilled water, hot water and gas requirements. The ESCo model, in this instance, meant no capital outlay required, reduced ongoing maintenance cost and reduced depreciation. These savings, coupled with reduced per unit energy cost, results in a net saving for A&L Goodbody of around €80,000 each year.

Currently, the trigeneration system is achieving operating efficiencies of over 80%. As a result, the natural-gas powered boilers run for just 5%-10% of the year (i.e. usually outside CHP’s standard operating times of 8am to 11pm Monday to Friday).

The CHP unit is completely synchronized with the national grid. If, for some reason, it cuts out, it automatically switches over to the grid. Moreover, because the unit generates electricity at the same frequency as the grid, the transition from one power source to the other is ‘flicker free’, so no damage is caused to computers or other sensitive equipment.

Average electricity generation output is currently totalling about 400 kW. Anything over and above the building requirements (usually about 1250 MWh annually) is exported to the national grid. At peak demand in winter (i.e. between 5pm and 7pm) half the electricity generated by the unit is exported; all export revenues accrue to CESenergy.


Just over two years after the commissioning of the trigeneration unit, A&L Goodbody remains enthusiastic about the move to the most advanced CHP technology currently available. It perceives the move as hugely beneficial – both in financial terms and in terms of minimizing environmental footprint.

Siobhan Conlon, Operations Service Manager, A&L Goodbody comments: ‘We are extremely happy with the CHP plant operating under CESenergy over the past two years. It has acted as our primary source of energy for our electrical, heat and cooling demands. The system also provides a backup generation to the building which is critical to the nature of our business. We have continuous saving on our energy costs and running costs of our existing chiller and boiler, as well as reduced maintenance and costs associated with back-up generation. We estimate these saving to be over €50k per year. The operation of the CHP plant has resulted in a substantial reduction in greenhouse gas emission which is in line with our company ethos.’

A lot of CHP units are either restricted in size to enable good heat utilization or operate at low efficiency rates. This trigeneration unit operates at 80% overall efficiency; this means that we need to dispose of no more than 10% of the excess heat generated throughout the year. We are very close to signing an agreement with some neighbouring businesses in the IFSC to channel the excess heat generated by our plant directly to those buildings.


Because of the high efficiency of this solution, it is estimated that A&L Goodbody has reduced its emissions by the amounts shown in Table 3.

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CESenergy is currently involved in projects in Ireland, Belgium, the UK and the Czech Republic. These projects range from a few 100 kWe CHP plants to 18 MW tri-generation district heating and cooling projects. In Australia, CESenergy’s sister company, Cogent Energy, is currently working on 50 MW of CHP trigeneration solutions. These projects will all be based on the ESCo model.

Our involvement in a range of countries and projects ensures that we stay on top of the latest changes in technology and continue to provide our customers with the highest standard of engineering, delivering the greatest financial return.

Brendan Marren is the General Manager of CESenergy, Dublin, Ireland.
e-mail: brendanm@cesenergy.ie

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