Solar Hot Water Systems Case Studies

ExtraCare, Hanover

Installed area - 78 m²

Peak output - 62 kW

Carbon dioxide avoided – 6.75 tonnes/year

Energy saving - 31,000 kWh/year

The ExtraCare development of 52 dwellings at Darcy House in Barking and Dagenham was chosen as a showcase for environmentally sustainable building technologies with a target BREEAM rating of Very Good.

The development consists of 16 bungalows and a two storey block with 36 flats.

Computer  modelling was used to help the design team to select an appropriate size for the Viridian Solar water heating system based on realistic estimates of hot water demand, renewable energy targets and value for money.

Hot water for the ExtraCare block was to be provided by a communal heating system in a ground floor plant room.  Two 800 litre cylinders, heated by gas boilers feed a circulating hot water loop from which the flats draw hot water.  The solar loop transfers heat from the 26 solar panels mounted on the roof and indirectly heats three 1,000 litre cylinders (the solar buffer).

Cold mains water is heated in the solar buffer tanks, which then feed the conventional heating system.  If the water from the solar buffer is hot enough, the thermostatic control on the gas fired heaters will prevent the boiler from firing.  If the solar buffer is not hot enough, the boiler will fire to lift the temperature to the set level.  

Communal Solar Array, Northpoint, Islington, London

Installed area - 75 m²

Carbon dioxide avoided – 5.2 tonnes/year

Energy saving - 30,000 kWh/year

Northpoint Islington is a development of 47 flats arranged over six storeys.  Fifteen of the flats are for an RSL client, the balance of 32 being available for private buyers. The development was required by the local planning authority to produce more than 10% of its energy on site from renewable energy sources. In order to produce the required proportion of the energy needs at Northpoint, solar water heating had to serve more than just the top floors - the design team calculated 2.4 sq m of solar collectors would be required for each of the 32 flats selected for solar heating.

The most common approach to solar heating design would be to link a dedicated solar panel to hot water cylinders in each flat. The problem was that the large number of insulated pipes (two per flat) would not fit in the space available for risers, and the design team disliked having such a high number of penetrations through the flat roof.  Also, heat losses from these pipes start to become significant as the distances increase - so occupants on the lower floors would suffer.

A conventional communal solar system addresses these issues, but creates 

new ones.  The solar panels are linked together and heat a large hot water store in a plant room.  This water is heated further (when necessary) by a fossil fuel water heater and distributed to each flat.  This approach brings the number of pipes from the roof down to two, and reduces the total number of solar panels needed to meet the target.  However, space for a plant room was unavailable, and the idea of charging occupants for hot water was unappealing.

Viridian Solar have developed a solar heating system that provides developers with all the benefits of a communal solar system without having to give up a large area for a plant room, enabling each flat to have its own individual heating system.

Panels on the roof of the building are grouped to serve flats.  A single pair of pipes run from the grouped solar panels and down the service riser.  Heated fluid from the solar panels is circulated to the flats in a loop on each floor.  Flow balancing components ensure a fair distribution of heat between every dwelling.

In each flat a control module monitors the temperature of the flow in the solar loop, and opens a valve to allow heat to flow into the solar heating coil in the hot water cylinder only when the temperature in the loop is sufficiently high to add heat.  The energy savings are optimised compared to individual solar systems due to “load sharing” - for example if the residents of one flat are on vacation, the other residents get to use their allocation of solar panel area.  The number of solar panels needed was reduced from 32 to 25 by the use of this system.

Grimsby Mental Health Unit

We were contracted and asked to provide a solution for a Solar Thermal Installation of ten panels on two buildings to provide hot water for a Mental Health Unit in Grimsby. The Schuco Solar Thermal System of 23m2 (in collector size) provides approximately 1000 litres of hot water per day.

Key Features

• Provides approximately 50 litres per m²
• Panel/collectors made with ‘Low E safety glass’
• High absorption of 95% (of solar radiation)
• High end quality German engineered system