Quarry case study: lake source was better than trench source
This customer approached us for a heat pump using horizontal trenches. When we visited the site it was a disused quarry, with rubble and waste making conditions difficult for creating good trenches. Instead we suggested taking advantage of the large quarrying hole filled with ground water, as this lake seemed to be a more viable source of energy for a Ground Source Heat Pump.
In the centre of the lake, the depth was almost 5m, so there would be excellent stratification resulting in water temperature remaining stable at approximately 4 degrees Centigrade in the coldest winter days, rising as the weather warms through spring.
After discussing the potential for the lake to be used and the issues of trenching on the site, plus the better system efficiencies likely to be achieved from it, the client agreed to proceed to calculations.
The proposed building's energy loads were calculated and the customer opted for first floor underfloor heating and low temperature radiators elsewhere. We worked with the client to ensure he correctly sized all of his heat emitters to get the best out of his Ground Source Heat Pump system.
The ground array design was completed and resulted in the need for three lake mats arranged on a supporting mesh. The position of the mats was identified by measuring the depths of the lake bed. The mats were towed to their position and the loops were filled, allowing them to sink to the bottom.
The heat pump was installed, with a 100 litre buffer vessel, linked to a 300 litre domestic hot water cylinder, and set up to prioritise the domestic hot water to ensure a constant supply.
Replacing a poorly designed system and saving 75% running costs
This client contacted us because of constant issues with his aging heat pump system. An early adopter of the technology, he had his heat pump installed in the early 2000s, but it had never lived up to expectations:
Using considerably more power than he had been advised
Producing low ground loop temperatures due to incorrectly sized ground collector and heat pump selection
Creating very high pumping costs because of the poor hydraulic design of the ground loop and considerable ice build-up on the ground loop pipe work in the utility room.
Over the years this customer had operated the system, the original installer had replaced the heat pump several times due to power issues, and had even (at his own expense) installed 3 phase power thinking that bigger was better and that 3 phase would stop the lights from flickering when the heat pump came on. Finally, the heat pump failed completely and the customer was ready to ditch the technology entirely and opt for LPG or oil, or have another go at a ground source heat pump.
The customer asked our advice and we carried out a detailed load calculation for the house, discovering that the heat pump was hugely oversized and the ground loop undersized. The heat pump was operating constantly at 55 degrees Centigrade (above manufacturers guidelines) to maintain the hot water tank temperatures and was cooled down to 35-40 degrees for the underfloor heating and radiators. The heat pump system also took up most of a utility room and a large part of an upstairs cupboard.
Having completed the load calculations, we produced a revised design. The result was a peak load of just 8 kW. The ground loop was replaced with a new system that was hydraulically balanced and correctly sized, the entire utility room pipe work was removed and replaced with new, the heat pump selected was a Mastertherm AQ22i single phase combi unit with an integral 170 litre hot water tank and a small 100 litre buffer fitted in behind the combi. The more compact installation meant that the customer could now have a washing machine in the utility room and gain back the cupboard on the landing.
The running costs for the heating and hot water have been reduced by 75%, the system operates as it should and the customer no longer has to adjust valves or settings to get the system to perform.
Redesigning the way water was handled in a sensitive central London location
An open loop ground source system was underperforming until Hex Energy designed a unique solution to enable water to be taken out from - and replaced into – the same well, fully supported by the Environment Agency.
Belgravia is one of London's most exclusive addresses, and unusually, has an open loop ground source heating and cooling system in a domestic property in Eaton Place.
We were brought in to find out why the system was not performing to the required level. What we found was that the water collection part of the system was working well, but returning the water (the discharge point) had become impractical. Without another suitable location to create a well, and with discharging the water to a drain being a wasted opportunity, we came up with a better solution.
From previous experience, we knew that it was possible to create a barrier which would enable the home owner to use the same well to take and return water, whilst avoiding heat loss.
A full visual inspection (CCTV) and geophysical log of the well was completed, to understand the strength of the chalk walls of the well. This identified the size and position of fractures in the chalk walls as well as a long section of unfractured chalk. A system was designed that would use a pump and a barrier and disperse the returned water into the fractures in the wall of the well at a different horizon to the abstraction area thereby creating vertical separation within the same water well. As a contingency, a motorised valve was added so that water could be diverted if heat loss occurred.
An important part of the project was liaising with the Environment Agency. They understood the unique aspect of the project design and agreed to allow the system to run for one season as a test, with data logged and reviewed afterwards. As it happened the installation year (2013) was exceptionally hot, with temperatures in London regularly exceeding 30 degrees.
We were able to measure that the innovative design worked perfectly, exceeding all expectations. The abstraction temperature remained a constant 13.4 degrees with discharged water at 19.7 degrees Centigrade. The spent water was proven not to be mixing, despite the high temperatures.