5.2. Domestic hot water and space heating and cooling
When looking for energy efficient solutions for space heating and cooling as well as water heating, it is seen that
there is a possibility of combining them together using high efficiency heat pump systems.
A number of solutions have been identified using geothermal energy but here two major problems were
encountered. Deep well geothermal systems would be strongly discouraged by the Malta Environment and Planning
Authority, since it would impinge on or risk the contamination of precious underground fresh water. On the other
hand, shallow-ground systems which would spread horizontally require large area, which is not available. Moreover,
if multi-level channels are made in the immediate underground base, the construction costs would increase as there
would be a need to build concrete pylons to support the building. However, some horizontal channels can still be
created to allow fresh air to pass through them before being introduced into the building. This is a standard
technology that is used in many countries. The advantage is that less dust and better conditioned temperatures can be
attained. The channels can also be coupled with an energy recovery unit, which would extract heat from or reject
heat to the exhaust air exiting the hotel.
Efforts have been made to explore the possibility of applying solar cooling, but this would require large roof
space area which was not available to place the solar panels. Moreover, the costs involved and the maintenance
required to build and operate such a small system would not be cost-effective.
The use of combined heat and power (CHP) generators is feasible but it does not produce renewable energy,
since the only types of fuel available would be diesel or liquefied petroleum gas. Once again, given that the hotel is
in a residential area, one would have to consider the micro-climate and how the introduction of a CHP engine would
affect it.
Solar heating has been considered favourably but it would have only produced hot water and it is not useful for
space cooling. Also, there is not sufficient solar energy in winter to provide both for water heating and space
heating. Moreover, the limited roof space would make this option provide only a fraction of the required energy for
the hotel. The same may be said for the use of solar photovoltaic systems, which are also less efficient than solar
heating, even though they produce electrical energy that is useful for all purposes.
Hence, due to space limitations, the need for flexibility in the use of energy systems, and the limited resources
available, the recommended option for this hotel was to use a solar photovoltaic installation combined with high
efficiency solar-ready heat pumps. This is a much simpler system than a solar thermal heating system as it requires
less piping works, pumps and water storage tanks. Moreover, its use can be changed depending on the season
(summer or winter) without worrying about problems such as over-heating or redundancy. From a technical point of
view, the use of solar photovoltaics with heat pumps has yielded similar performance than using a solar thermal
heating system alone, as found from the use of Polysun software (11,705 kWh/year compared to 11,525 kWh/year),
but requiring much less maintenance and infrastructural changes, thus making it a more attractive option to the user.
The system is shown in Fig. 7, as proposed by a supplier [12].