Heating, Ventilation and Air Conditioning. Although aquaponic farming is based primarily on the flow of water, these three operations are vital to the successful circuit of our system, especially as we are growing inside a warehouse. Much like the balance of fish food to plant uptake of nutrients, these factors must be kept in equilibrium to ensure the best growing conditions possible.
As a result, our HVAC Unit is really quite complex (which is accentuated by the fact that it looks like a futuristic space ship). The hydroponic grow room and aquaculture area with the fish tanks require different temperatures and humidities (which is where the insulating inner wall comes in).
The fish tanks need to be kept at 26°C, so in order to keep this water temperature stable we want the temperature of the air to stay warm too. By keeping the room and the water at a similar temperature we can also reduce evaporation from the tanks. Whereas in the grow room, we want an air temperature of 22°C and a humidity of 80% for our plants to grow at an optimum rate. Furthermore, the LED lights that we use to grow the crops generate heat, so we need to have a constant air flow over the plants to maintain their transpiration and ensure that the temperature and humidity at crop level is consistent.
Air will be blown over the grow beds…
…and pumped into the aquaculture area.
The air that is blown over the crops in the grow room by the HVAC system pushes out this warmer air, which is blown into the aquaculture area.
After the air has passed through the aquaculture area, it goes through a heat exchanger.
This captures the heat from the air and does two things.
Firstly, it circulates a small quantity of warm air back into the aquaculture area to maintain the higher temperature there.
Secondly, depending on how cold the temperature is outside, the heat exchanger tempers any fresh air that is drawn into the system by passing hot air (from inside the warehouse) over cool air (from outside) to warm it. The unit we have has an 85% efficiency which essentially means that 85% of the heat in the warm air can be transferred to the cool air, minimising heat loss. This fresh, colder air allows us to supplement the chiller system which cools the air in the farm to be pumped back into the grow room. In this way, we increase the efficiency of the cooling system and use less energy to power it.
Copper piping facilitates the heat exchange
Air is expelled from the warehouse and fresh air drawn in from outside
The HVAC system is fully automated..
…and is controlled by the air handling unit.
From here the air is then passed back over the crop in the grow room and the system continually recirculates. In total the air inside the hydroponic space will circulate through the Air Conditioning System four times an hour, and as it recirculates up to 10% of it will be replaced (per hour) by fresh air from outside.
Including free cooling in our system allows us to use a lot less energy to heat and ventilate the farm. We’ve worked with international engineering firm Arup to optimise this, and the results of their energy modelling found that by replacing 10% of the air volume in the growing room with fresh air every hour we can reduce the energy use for heating, cooling and dehumidification by 50% compared to a system that uses no free cooling.