Cooling with Heat Pumps & MVHR
Heat pumps are primarily used for heating; however, they also offer significant cooling capabilities when integrated with Mechanical Ventilation with Heat Recovery (MVHR) systems, provided the MVHR is designed with cooling in mind. MVHR systems are ventilation systems that provide a continuous supply of fresh, filtered air to the habitable rooms in the building, at the same time extracting damp stale air and odours from kitchens, bathrooms and utility spaces. The core component is the heat exchanger, which transfers heat between the outgoing stale air and the incoming fresh air – heating the incoming air if it’s cooler than desired, and cooling the incoming air if it’s warmer than desired, this reducing the amount of energy needed to keep the building at the desired temperature. More advanced MVHR systems include a cooling coil (a “powered” heat exchanger) which utilises chilled water from an external cooling source, potentially an Air Conditioning unit, but ideally a reversible heat pump, to actively “chill” the incoming fresh air.
Stiebel Eltron Air Source Heat Pump
Airflow Entro MVHR unit
- Year-Round Comfort: These systems provide both heating and cooling to ensure the temperature in the building is as desired throughout the year.
- Energy Efficiency: Both MVHR and heat pumps are energy-efficient, significantly reducing energy consumption compared to traditional HVAC systems. A heat pump typically delivers 3-5 kW of heating (or cooling) for every 1kW of electricity. An MVHR systems typically recovers around 90% of the heat energy from the air being expelled.
The benefits are clear; however, it is crucial that the MVHR system is designed by someone who understands how to design an MVHR system that is to deliver cooling, specifically, how to design an MVHR that can move double the amount of air than is required for ventilation only. Many installers of MVHR will quote the temperature of the air that will be expelled from the ducting outlets, but if the volume of this cool air is insufficient, the effect on the room temperature will be minimal. It’s the amount of air as much as the temperature of the air that determines whether the system will actually cool the building.
To move more air without exceeding acceptable (and mandatory) acoustic and energy consumption levels usually requires a larger MVHR, with bigger pipes, and more ducting. Unless the MVHR is designed correctly, the system won’t cool the building, at best it will just slow down the speed at which the building heats up…
Another consideration, is the need for an “umbrella” control system or Building Management System (BMS) that manages these disparate heating/cooling/ventilating systems. Without a BMS, switching between heating & cooling involves manually changing settings in the three systems. If all the systems are in cooling mode, and the temperature of the domestic hot water (DHW) tank falls below the set point, perhaps because people take showers, then the heat pump will automatically be asked to reheat the DHW cylinder, but the heat pump cannot heat and cool at the same time, so what happens – either the cooling or availability of hot water will be compromised? An automated BMS managing the heating and cooling systems prevents the heating system trying to heat the property at the same time as the cooling system is trying to cool it – which is more common than you might expect and not good for energy efficiency!
Combining MVHR and heat pump systems offers a highly efficient and sustainable solution for managing the temperature inside modern buildings. By leveraging the strengths of both technologies, it is possible to achieve a comfortable indoor environment with reduced energy consumption and improved air quality. The long-term benefits make these systems a worthwhile consideration for both residential and commercial applications.