Office building of Universidad Politecnica Valencia

The purpose of this project was to design, install and use a ground source heat pump system in mixed climate applications, where cooling requirements are dominant, in order to obtain reduced energy consumption for the same cooling and heating performances as opposed to a conventional air-to-water heat pump. The detailed comparison between the systems that was performed shows that the geothermal system saves 41 % in terms of primary energy consumption in heat mode while a minus of 38 % was measured for cooling mode as opposed to the traditional heat pum system working under the same climatic conditions and same loads as well.

Project description

Building, overall energy concept

The ground source heat pump together with 12 air conditioning coils are installed in an academic building at the Universidad Politecnica de Valencia, Valencia, Spain. The total air-conditioned area comprises 250 m2 and includes a corridor, nine offices, a computer room, and a chamber with photocopiers and a coffee dispenser. All rooms are equipped with one or two fan coils except the corridor.

Photo 1: View of the academic building with office and chamber with photocopiers

Loads were calculated by means of standard software (based on the BLAST [1] load calculation approach) taking into account the load profile variations during the whole season in heating and cooling mode. Load peak values in heating and cooling modes were sized at 15 kW and 17 kW respectively.

The experimental implementation of our GSHP system is intended to perform a quantitative assessment of savings, from the energy efficiency point of view, with respect to a conventional system. An air source heat pump was chosen as reference system since it is widely used in commercial applications in the South European region. In order to compare both systems we have established analogous operating conditions on both systems, linking them to the same building and thus to the same heating and cooling load conditions. The structure of the GeoCool installation is shown in a schematic diagram. This experimental design allows switching from the air-water heat pump to the ground coupled heat pump.

The geographical location of Valencia is: Latitude: 39,48ºN, Longitude 0,38ºW, Altitude 20m. All climatological information of the area of Valencia has been gathered in the Atlas Climatico de la Comunidad Valenciana (Perez Cueva, 1994). The region of Valencia is part of the Mediterranean Area, with moderate winters and fairly hot summers. The main characteristics of this climate are the clear dry period in summer. An overview of the medium temperature T, the mean maximum temperature TM, the mean minimum temperature Tm, the absolute maximum temperature (MAXabs) and the absolute minimum temperature (MINabs) over one year is shown in a graph. The overall thermal load for heating is 22 kcal/h while the overall thermal load for cooling is 15 kcal/h.

The results of a detailed theoretical study comparing the two heat pump systems considered are summarised in a separate document.

Heat pump system

A water-to-water heat pump is used modified for using propane (R 290) as refrigerant. The unit from which the design of the propane heat pump was developed is a reversible water-to-water heat pump of CIATESA (model IZE-70) with nominal values 15.9 kW and 19.3 kW of cooling and heating capacity respectively.

Photo 2: Overview of the machinery room

The UPV Air Conditioning system consists of three main components: internal loop, external loop and a heat pump as described above.

• An indoor loop consisting of a series of 12 parallel connected fan coils, a circulating pump, a storage expansion tank and the corresponding piping. The loop serves and distributes the chilled water (cooling mode) produced at the heat pump to each of the fan coils.
• An outdoor loop with the ground heat exchanger (GSHX), a circulating pump, a storage tank and the corresponding piping. The loop takes the heat exchanged at the pump (cooling mode) and dissipates it to the ground. The GSHX consists of six boreholes in parallel of 50 m deep each, containing a polyethylene “U” pipe. The borehole diameter is 150 mm. Each borehole has a different grouting or separation technology. Their individual characteristics are described in Figure 1.
  
  Figure 1: Ground Heat Exchanger (GSHX).

Operation experiences

Measurement Campaign (heating/ cooling seasons):

The data acquisition system was designed to characterize the system performance. To this purpose, different system parameters like water temperature, mass flow and power consumption were measured. A network of 44 probes was setup to allow monitoring the most relevant thermal and flow parameters of the internal hydraulic group, the external hydraulic group, both heat pumps and the ground. The probes at the internal hydraulic group measure quantities needed to calculate the heating and cooling capacity supplied by both systems. There are two temperature probes placed at the connection point between both AC systems and the building. These probes measure the temperature of the water entering the fan-coil system and the temperature of the water leaving the fan-coil system. There is also a Coriolis meter registering the mass flow in the internal hydraulic group.

Experimental measurements at the UPV facility during one year have provided a considerable amount of information about the system performance. In this work we have focused particularly on the evaluation of the energy efficiency of an air conditioning system based on ground coupled heat exchangers compared to a conventional air source system in heating and cooling modes.

The results of the study allowe to draw the following conclusions about the operation of both systems:

• For the whole heating season the geothermal system saves, in terms of primary energy consumption, an average of 41% of the energy consumed by the conventional one.

• For the whole cooling season, the average saving obtained by the geothermal system was 38% of the energy consumed by the conventional one.

Costs, economic efficiency, incentives

No information available.

Regulations, guidelines, benchmarking

No information available.

References

Bibliograhic references (Reports, journals)

[1] Pedersen, C.O., D.E. Fisher, R.J. Liesen, J.D. Spitler, Load Calculation Principles, American Society of Heating Refrigerating and Air-Conditioning Engineers, Inc., 1998.

[2] Lund JW., Freeston DH. World-wide direct uses of geothermal energy 2000. Geothermics 2001; 30:29-68.

[3] Lund JW. Ground source (geothermal heat pumps. In: Lineau PJ, editor.

[4] Course on heating with geothermal energy: conventional and new schemes. World Geothermal Congress 2000 Short Courses. Kazuno, Tohuko district, Japan: 2000. p. 1-21.

[5] Martin PE. A design and economic sensitivity study of single-pipe horizontal ground-coupled heat pump systems. ASHRAE Trans 1990;96(1):634-42. Energy Star Program from the US Environmental Protection Agency (http://www.energystar.gov)

[6] Sanner, B., Karytsas, C., Mendrinos, D., Rybach, L. Current status of ground source heat pumps and underground thermal storage in Europe. Geothermics 32 (2003) 579-588.

[7] Pedersen, C.O., D.E. Fisher, R.J. Liesen, J.D. Spitler, Load Calculation Principles, American Society of Heating Refrigerating and Air-Conditioning Engineers, Inc., 1998.

¹ Primary Energy Ratio: Useful heating (and cooling) energy delivered / primary energy input (kWh_UE / kWh_PE)
² PEER=annual heat delivery/primery energy demand=SPF/fPE, fPE=Average European primary energy factor: 2,35 kWhPE/kWhel
³ Average European CO2 factor for electricity: 0,45 kg CO2/kWhel