Net ZEB Case Studies - Modeling, Design, and Optimization of Net-Zero Energy Buildings - page 387

A recirculation system provides hot water in order to reduce water waste. A
glycol-water mixture transfers the heat from the solar collectors to the coil
of the storage tank.
Figure 7.29 shows a simplified scheme of the geothermal probes and the
heat pump. The manufacturer stated that the nominal GHP has a COP of
4.6, but the monitored value is lower. The efficiency reduction is due to
- the nonoptimal setup of the controllers;
- the anomalous electrical consumption of the compressor with respect
to the declared data (7-8% higher);
- mismanagement of the ignition system characterized by short cycles.
Fig. 7.29 Scheme of GHP system
The geothermal circuit is connected to the free-cooling heat exchanger
during the summer season. A grid-connected PV system (20 kW peak
power) generates electricity for the LH. The PV array, made of 115 panels,
covers the entire roof surface (150 m 2 ). It faces south with a 21° slope. The
panels are arranged in nine strings and connected to three inverters. The
nominal efficiency of the PV panels is 12%.
In each flat there is a radiant floor connected to the GHP. The room air
temperature is controlled by the regulation of the water flow in each tubing
loop. In the summer, cooling is mainly provided by the GHP and, to a
small extent, rooms can be free cooled with the water provided by a ground
coupled heat exchanger, during the start-end of the cooling season. Cold
water is supplied in the range of 15-18 °C through the use of mixing valves.
The supply water temperature for space heating is between 25 and 28 °C.