University College Bergen

Back in 2005 we started at Opticonsult, now Sweco Bergen to work on the design and the solutions for the coming new university college in Bergen. A consept that we desided very early, was that all energy should be kept within the system, if at all possible

Off course quite a large portion of the energy would leak out through walls, windows and doors, but surplus energy, as cooling energy we would keep, and to a large extent recircle, either directly or by dumping into a borehole system during the summer, heating the ground and then in the winter use the borehole system as the heat source for a heat pump.

A major challenge here was the difference in heat rate when dumping and extracting heat. We found that the optimum size of the heat pump would be a heat delivery of app. 625 kW, where the gross heat demand was app. 2 775 kW. A heat pump of this size needs app. 483 of heat on to the evaporator. We are using high efficiency ammonia heat pumps having a COP of 4.4. The low temperature heat demand of 483 translates into 81 boreholes of 200 m length.

The cold demand on the other hand was found to be 2 900 kW, again using ammonia we have a EER of app. 5.5, giving a heat dump of app. 3 430 kW. To be able to dump all this heat into the gound would require 172 holes of 200 m. As we can se the difference in requirements is quite substantial.

Typically you would have designed the system as can be seen in the figure below.

Typical system design when the heat dump and heat demand are not aligned when switching from cooling mode to heat pump mode.

Designing a system like that wouldn’t be consistent with the overall design philosophy, so we started looking into how to reduce the need for heat dump. The first thought of course was to reduce the cold demand, but the representatives of the users were quite clear that that would not be acceptable at all.

Another possibily then was to use an industrial approach, which is to break the bond between demand and production. You do that to produce cold to storage and then letting the cold distribution system pull cold from the storage when the production capacity is lower than the demand. To determine the size of the storage we had to examine the distribution of cold demand during a full 24 hour cycle

Cold demand over design 24 hour cycle (nychthemeron)
Cold demand and production during the design 24 hour cycle

By using a cold storage based on substance that melts at 10°C we could reduce the cold production capacity from 2 900 kW to 1 400 kW, a reduction of 52%. This in turn means that the borehole requirement was reduced from 172 to 83. As you probably will have forgotten, the optimum borehole system for the heat pump was 81 holes of 200 m. By increase the length of each borehole by 5 m we reached the size required for both heat dump and heat pump.

Cold storage tanks going in. 4 pcs. of 62,5 m3 each.

By designing the system like this, we achieved a system where all the surplus heat from cold production is pumped into the ground. There are no drycoolers in this system, something that especially the architects were very thrilled about. Later in the process we had the idea that indirect evaporative cooling could further reduce the cold rate demand. (At this time I was told in no uncertain terms that I should STOP coming up with ideas). This further reduced the cold demand with 500 kW, something we where very chuffed about. An unexpected side effect though was that it reduced the capacity of the heat pumps as not so much heat was being pumped into the ground.

The University College Bergen is expanding their building mass by app. 11 000 m2, and due to these design features it doesn’t need a cold production system of it own, but can be hooked up the existing system, as it has enough capacity due to the 500 kW reduction we found by using indirect evaporative cooling.