In a modern hybrid heat pump, solar heat can be used nearly all year round with very high efficiency, even in a Nordic climate. By controlling the solar heat where it is most beneficial, the utilization rate will increase, partly because the number of operating hours increases over the year, but also because the solar circuit can work at a lower temperature, which will increase efficiency. In a hybrid heat pump - like the HYSS system - the annual performance factor for both heat and hot water will reach 5-7, which is almost twice as high as the most recent test of conventional heat pumps on the Swedish market (Swedish Energy Agency 2012-215).
A heat pump collects heat from the bedrock, ground, lakes (watercourse) or the outdoor air and it has four main components. The construction is built around an evaporator and a compressor as well as a condenser and a throttle valve. The heat that is extracted from, for example, a drill-hole is transferred to a refrigerant, which vaporizes when energy is absorbed. The compressor increases the pressure of the refrigerant gas, which significantly raises the temperature. When the refrigerant is condensed and turns into liquid, heat will be released which is used for heating purposes and hot water.
A geothermal heat pump collects heat from the bedrock and groundwater with a circulating liquid (brine) in a collector tube. The drilling depth is adapted to the building’s heat demand (power and energy requirements) and will normally vary between 120 - 200 meters. There should be at least 20 meters between the boreholes so that they do not affect one another or cool each other down.
HYSS – Hybrid Solar System – returns solar heat to the borehole, which reduces heat output and also keeps the borehole at a more consistent temperature. The solar heat also raises the temperature of the brine, which in turn increases the heat factor (efficiency) of the heat pump. In most cases, HYSS heat pump becomes twice as effective as conventional geothermal heat pumps.
The ground source heat pump collects heat from a collector tube in the ground. The tubes should be in frost free depth, in other words, 1.0 - 1.5 meters deep. The distance between the tubes should be at least 1.0 meter to be sure that they won’t affect each other. The length of the tubes must be adapted to the building’s power and energy requirements for heat and hot water. A conventional single family home requires 300-600 meters tube length.
The HYSS system returns solar heat to the tube in the ground, which increases capacity output over the year while the temperature of the brine rises, improving the performance of the heat pump.
In cases where the length of the tube can be extended and isolated, such as if it is placed under a concrete slab during a new construction, it is possible to store solar heat seasonally, from summer to winter. This type of ground heat storage is called ASES (Active Solar Energy Storage) and it means that a solar heater’s surplus heat from the summer can be stored for winter and used in a heat pump. A HYSS system in this type of system gets an annual performance factor of a little over 8, i.e. 1 kWh of electricity provides 8 parts of heat and hot water.
An air to water heat pump takes advantage of the heat content of the outdoor air. The air heats up the brine and then the refrigerant, which is then vaporized and condensed in the same way as in a geothermal or ground source heat pump. The efficiency is generally lower for an air to water heat pump and it is therefore more suitable in the southern regions of the Nordic countries and especially by the coast where the annual average temperature is somewhat more consistent and higher than inland.
HYSS – Hybrid Solar System – can be connected to an air-outdoor unit that uses the same refrigerant and that can be combined with a shorter ground heat loop or a shallower borehole. This is a way to take advantage of the benefits of increasing the brine temperature with an air to water heat pump. Excess heat from the sun collectors can also be transferred to the shorter ground loop.
A lake heat pump works the same way as a ground source or geothermal heat pump. Instead of collecting the heat from a borehole or a loop in the ground, a collector tube will be used on the bottom of a lake or pond. The tube is kept in place with weights. The length of the tube is determined by the power and energy requirement of the house for heat and hot water
As in all other HYSS systems, solar heat increases the temperature of the brine circuit and this also happens in lake heat pumps. The increase in temperature from the solar heat raises the heat factor and basically makes the heat pump technology twice as efficient as conventional systems.