Marko Granroth, lecturer from KTH in Sweden, talked about various types of ventilation systems in residential buildings using extract and supply air system in a combination of air handling unit and heat exchanger. He shared his experience on mechanical ventilation systems from Sweden during Swegon Air Academy seminar in Tallinn on November 22, 2013, with topic on Modern and energy-saving concept in small residential buildings.
Mechanical ventilation or “forced” ventilation is used to control indoor air quality via volume or pressure, where volume control is when the volume is constant and pressure will vary and air flow is fixed, and in the pressure control is when the pressure is constant and volume will vary and air flow will be pressure-controlled.
The multi-residential buildings (apartment buildings) have three systems as described below.
1. Extract air system with an air handling unit in the basement and supply air through the facade
The first system Marko described is the extract air system with an air handling unit in the basement and supply air through the façade with energy recovery using heat pump. This system may have problems with noise in supply air devices located in outer facade (cheap but working). The supply air goes through the cold facade to the interior and passes behind the radiator and in this way is preheated before it enters the room. This simple ventilation system with energy heat recovery is not to be used in buildings located by noisy road. Also the engineer must think about fire protection with active system where sensors can detect fire in a specific apartment and via ventilation control (fire exhaust fan) the fire goes always out from that specific apartment.
2. Extract air system with an air handling unit in the attic and supply air through the facade
The modification of the first system is an extract air system with an air handling unit in the attic and supply air through the façade. This system has easier maintenance purposes, but it may require a larger radiator surface at places where the outdoor air is brought in and there is a possible risk of draught in the winter and also it places greater demands on U-value for the façade. As for fire protection method, the smoke spread is relieved through the duct system pressure and damper in combination with stopped fan. This extract air system with supply air by facade preheated by radiator has no heat recovery (cheaper, but energy price goes up, fire problem) and it is forbidden in Sweden because it has no heat recovery, as there are demands in place that all building in Sweden must have heat recovery now.
3. Supply and extract air system with energy recovery (AHU with heat exchanger) in the attic
This system has less noise problems as there are no supply air devices in the façade. If the extract hood in a kitchen is connected to exhaust air, than the cross heat exchanger might be more preferable, unless the rotary heat exchanger (as another choice) has good management of odours treatment. The fire protection is solved via active system converted to exhaust with standard exhaust fan in operation with relieving the supply and exhaust air systems.
Marko stated: “The system with supply and extract air with heat recovery with exhaust and supply in an apartment is the most commonly used. On one hand the rotary heat exchanger is highly energy-efficient but it might have problem with smells and you have to check the balance in ventilation and you need a technician to fix it, and also there is an issue with preventing passing the smells from cooking. On the other hand the cross flow heat exchanger doesn’t have any smell problems but lit is less efficient).”
Small single- and double family (small residential) houses can use one of the following systems.
1. Extract air system with heat pump
The extract air system with heat pump supplies ventilation and heat is supplied by a traditional hydronic heating system (radiators) in a combination with a heat pump (with energy heat recovery) supplying the heat. Supply air device is located in the façade. Extract kitchen hood has its own bypass ducting.
2. Extract air system with heat pump with bypass of exhaust from kitchen hood
The system is similar to the one above, only the extract kitchen hood is connected to the ventilation system.
3. Extract air system with heat pump and electric radiators with central building control
The source of heat are electricity and heating of domestic water to an exhaust air heat pump. The energy is recovered through the exhaust air via the heat pump on air/water side.
4. Supply and extract air system with heat pump and radiators
Heat is supplied with traditional hydronic heating system.
5. Supply and extract air system with heat pump and floor heating, or in a combination of floor heating and radiators as system number 6
At the end of his presentation, Marko has given few interesting advices. One point was about an engineer error which may result in a wrong design and a contractor decides to change the engineer´s plans in order to improve it and save some money. This may results in 5% saving but in an unhappy client.
The most common problem in small buildings is that the system works but a heat pump is 2.5 m high but the door has only the height of 2 m, and if the heat pump breaks down, then the cost of taking down the wall to fit it a new heat pump can sum up to 1,500 EUR.
Marko has finished his speech by saying: “The most important is the understanding of an issue, not just facts and figures.”