Innovative Technologies and Applications

Concepts for Energy Efficient Cooling

  Case Studies

Absorption chiller installation in a hotel

 

The installation of a YAZAKI model WFC 30 absorption chiller was found to be economical for a building air-conditioning application in a 5-star hotel. The concept considers a system being driven with waste heat from a planned biogas cogeneration unit in the vicinity. A power-heat coupling is desirable for the cogeneration unit to operate economically, as this raises the feed-in remuneration for the electricity produced by 2 euro cents/kWh (3 euro cents/kWh starting from 2009) in accordance with the German Renewable Energy Sources Act (EEG).

In this context, hotels represent ideal consumers due to their year-round heating demand, a significant share of which (up to 40%) is used to supply hot water. As a result, the cogeneration unit can be operated in this case with estimated 6,857 full load hours per year (with complete waste heat utilisation). The use of an absorption chiller to cover the basic load for the air-conditioning of the hotel rooms shifts the heating demand as shown in the diagram. This raises the number of full load hours of the waste heat utilisation by 960 h/yr and increases the annual cogeneration bonus by €15,490 per year. For the economic efficiency of the concept, the following assumptions were made:

  • The investment cost of the cogeneration unit will be covered by the basic remuneration of the German Renewable Energy Act (EEG). The additional costs of the concept (bio-gas pipeline to the hotel, installation costs) can be paid back in less than 3 years through the cogeneration bonus for the heating and hot water heat demand.
  • As the cogeneration unit is operated year-round at the hotel, the use of the absorption chiller incurs no additional operating costs for the cogeneration unit - no additional sales revenues are required for heat output in the summer.

 

As the maximum electrical consumption of the hotel in the summer results from the cooling, the hotel can also be charged a corresponding share of the demand charge. Given these initial conditions, the hotel operator achieves an amortisation period of 4,7 years for the total investment of approximately €63K required for the absorption chiller and the expansion of the cooling towers. The operating cost benefit does not take into account the additional revenues from the increased cogeneration bonus totalling €15,490 per annum.

Hotel:

  • 530 rooms, gross floor area 36,000 m2
  • Cooling supply via 3 vapour-compression refrigeration units totalling 700 kW, COPvcru = 3

 

Cogeneration unit:

  • 537 kWel , 524 kWth (ηges=0.79)

 

Absorption chiller (WFC 30):

  • Cooling capacity at design: 127 kW
  • Peak load covered by existing vapour-compression refrigeration unit, - Interest rate 5%
  • Electricity unit price €0.12/kWh, demand charge €100/kW
  • Water €2.50/m3

The specific example shows that there are most attractive situations that favour the use of absorption chillers. A short amortisation period can even be achieved for a subsequent installation if a low price per kWh for the driving heat is available. In the case of a new investment directly compared versus an alternative investment in a vapour-compression refrigeration unit, the benefit is even greater..

 

Absorption chiller

Vapour-compression refrigeration unit

Difference

Maintenance / repairs

 1.763 €/a

1.500 €/a

+ 263 €/a

Electricity costs

278 €/a

12.100 €/a

- 11.822 €/a

Demand charge Electricity

50 €/a

4.233 €/a

- 4.183 €/a

Water costs Cooling

+ 513 €/a

Cost benefit absorption chiller

15.229 €/a

 

 

Analysis by Perpendo GmbH für Energietechnik und Verfahrenstechnik, Aachen