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Super-efficient heating and cooling

17.4.2015

Derby Business Park is a group of three modern office buildings which was completed in 2012 in Espoo, north of the Finnish national road 1. Among others, the headquarters of Siemens and the construction company SRV are situated in the buildings.

The heating and cooling of the buildings, the cubic content of which spans 80,000 m3, are carried out with a super-efficient ground heat system which was designed and customised specifically for the special needs of the site.

Background

The construction company SRV was designing their own headquarters and wished to discover the most efficient manner of heating and cooling the building, taking into consideration both the expenses and the environmental impact.

Best solution discovered in preliminary enquiry

At the end of 2009, Konsulttitoimisto Enersys Oy received a commission from SRV to conduct a preliminary study concerning heating and cooling options for SRV’s new project.

In the extensive preliminary study, different heating and cooling options were examined, and the usability of different natural sources of heat were also investigated. On the basis of the enquiry, the most affordable primary alternative, considering its life cycle impacts, proved to be a combined heating and cooling system based on heat pump technology, where the bedrock underneath the plot is utilised as a source and store of heat.

Oil burners were selected as a source of additional and auxiliary heat, as the need for additional heat was calculated to be very small and oil burners do not entail fixed charges.

Geothermal energy field – a production investment which will provide decades of utility

The single most expensive part of the system is the geothermal energy field comprised of the energy wells bored into the bedrock. It is advisable to size the system very carefully, as the field should be functional for at least 50 years. Oversizing a geothermal energy field may be more expensive in the investment stage, but undersizing may ruin the entire operational and financial foundation of the system.

A basic study was ordered from the Geological Survey of Finland (GTK) to investigate the properties of the bedrock, such as thermal conductivity and initial temperature, with the use of test holes.

The properties of the bedrock, the heating and cooling loads of the project, and the placement of the bore holes affect the long-term temperature development of the bedrock located in the sphere of the energy field’s influence. This temperature trend substantially affects the functionality and the operational economy of the system, which means that the system should always be designed with a controlled and predefined temperature development of the ground.

operationyears

An example of a long-term temperature trend in the geothermal energy field which should be controlled and defined in the planning stage.

The significance of design

The metaphor of the weakest link is very true in heat pump systems. The main components of the system are:

Heat sources – HP plant – Load/distribution networks

The weakest of these dominates the functions of the entire system, and it has been proven that the difference in life cycle expenses between systems operating well or poorly can be higher than the initial investment. It is advisable to design the system as an entity in order to ensure the compatibility of different parts and avoid weak links.

It is also recommended to start designing the ground heat system in the early stages of project planning to take the functions of the system sensibly into account as a part of the overall planning of the construction project (the placement of the energy fields and equipment facilities and the phasing of construction can result in large savings).

Enersys was in charge of the overall design of the ground heat system and a design agency specialised in housing technology was in charge of planning the heating and cooling networks. Ensuring the compatibility of the systems required close cooperation between the ground heat and housing technology designers. The cooperation was extremely successful in this project, and the functionality of the networks has been deemed optimal.

In addition, it was decided to apply for a LEED certification (Leadership in Energy and Environmental Design) for the project to reduce the environmental impact during the use of the buildings. This also set special requirements for energy efficiency.

 

Resulting in a super-efficient, customised station

To minimize life cycle expenses and adhere to the strict energy and emission requirements, a completely customised heat pump system was designed for the needs of the project. The system includes the following parts and equipment:

  • Customised primary heat pump units, power 2×250 kW for both heating and cooling, measured annual efficiency over 4.0
  • Customised high-temperature unit for producing heated service water, heat source cooling, measured annual efficiency 3.5
  • Separate water cooling unit, condensing to energy wells
  • Energy wells 24×300 m, special collectors

Very strict performance characteristic requirements were drafted for the heat pump equipment in advance. On the basis of competitive bidding and careful evaluation, the Finnish manufacturer Pemco Oy was selected as the supplier. The performance characteristics of the equipment delivered by Pemco were measured in the implementation stage and they were discovered to even exceed the strict performance characteristic requirements.

pemco

Savings and profitability

The system was implemented in the autumn of 2012 and has been monitored since. When calculated using the market prices of electricity, the usage expenses of heating and cooling have totalled about EUR 40,000 per year (VAT 0%) during the first years of usage. The need for heating has been so far 1,700 MWH per year and the need for cooling connected to the system has been 700 MWH per year (some accounted by cooling the server space), whereupon the average price of the produced heat has been EUR 20 per MWH and that of the cooling
EUR 6 per MWH. Therefore, the system enables savings of EUR 2 million during 25 years (at current price levels), compared to a regular heating/cooling system in accordance with the image below (or EUR 5 million during a 50-year life cycle). As energy prices rise, the savings are increased as the rising prices do not affect the free energy of the ground heat sources; the share of free energy has been 3/4 for the heating alone.

lifecyclecosts

With the help of a well designed and implemented ground heat system, it is possible to reach life cycle savings that are multiple compared to the initial investment.

The savings are based on the maximised energy efficiency and optimised production structure of the system. Most of the energy comes free of charge from the bedrock or as a side product of cooling. The image below presents the production distribution of heat in 2013–2014.

pie

The end result was not accidental; instead, it was made possible by controlling the implementation chain of the entire system from the beginning to the end:

  1. The best system is selected as the premise for design through a neutral preliminary study
  2. The system is designed specifically for the special requirements of the project, eliminating weak links in the planning stage
  3. Detailed procurement definitions are drafted and the offers are evaluated with life cycle benefits (not the price) as the main criteria.
  4. The work of the contractors is sufficiently monitored and the compliance of the plans is ensured
  5. The end result is ensured with a thorough deployment and the users are trained for efficient usage.