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A hybrid ventilation solution for a multi-functional building
Case studies
January 7, 2014

A hybrid ventilation solution for a multi-functional building

The presented Engelsons office building built in 2009 could be considered as a multi-functional building with the indoor climate conditions controlled by a hybrid ventilation system of air and water. In this hybrid system there are two methods of ventilation and heating/cooling: first with air diffusers with constant air flow and second with climate beams with demand-controlled on water side and constant air flow on air side.

The building is used as offices, a warehouse and a store with packing area. During the design process the choice was to use a solution which merges energy efficiency and high standard of indoor air quality (IAQ) with the constant monitoring of temperature, humidity and energy consumption.

The building is made from steel and concrete structure with well-insulated building envelope in order to reduce to the thermal losses to a minimum. The windows are of good materials and there is solar shading system in offices.

Building systems

The building can be split in 3 zones where each zone is served by an air handling unit (AHU 1, 2, 3). Zone 1 is rented out as offices to a third party, zone 2 is a warehouse, and in zone 3 are offices and a store with packing area. Both office areas (zone 1 and 3) are heated and cooled by climate beams which are demand-controlled on water side and these two zones are served separately by two air handling units  And in the common areas (corridors and such) in office zones are installed air diffusers with constant air flow. The store is heated by air diffusers with constant air flow and cooled by climate beams (demand-controlled on water side and constant air flow on air side). The packing room is air-heated via air diffusers and cooled with a climate beam (demand-controlled on water side and constant air flow on air side) above the work desk. Furthermore in this packing area, a split system is installed to compensate the heat peaks during summer. The warehouse is heated only by the air diffusers especially designed for large spaces.

Ventilation

In the building there are three air handling units (AHU) installed, one for each zone, but only the AHU 3 which serve the offices and store with packing area is monitored constantly. Each AHU is equipped with high efficiency rotary heat recovery which allows the pre-heating of the fresh air with exhausted air. The air flow rate depends on the difference of measured pressure between supply and extract air,  and in this way the building pressure is ensured to be at the required value.

The ventilation system is a constant air volume system (CAV on air side and DCV on water) and in some large rooms there is the possibility of boosting manually air flow to double amount of the supply air. This function allows defining these areas as a system with variable air volume (VAV).

The AHU 3 which serves offices and a store with packing area works 24/7. However between 6:00 and 19:00 it delivers supply fresh air and heating, during night time it switches its function in night-mode.
Without people inside the building there is no need to supply fresh air, yet at the same time there is a need to heat the building in order to avoid too large temperature drop. How can this objective be reached without wasting energy?

If one considers a winter night: as there is no need to supply fresh air in the building, the night-mode allows the energy saving by recirculation of indoor air, already at 20°C. In this way the temperature difference between the recirculating air and the water in the coils is lowered. It means that the power supplied to the air is lower as well as the energy needed for heating of air flow from 14°C (after the recovery) to 20°C. In addition this will allow to decrease the temperature by 2°C, in other words the extract air has to reach 18°C before the heating system increases the thermal power of the water flow rate. Of course, during the transitory of night and day there will be a need for an increase of energy consumptions for the AHU to restore the operative indoor day conditions.

The energy saving is increased if one considers the particular design of the AHUs in which a bypass section significantly reduces pressure drops, this means less energy consumption by fans.

Production of energy

The heating is furnished by a ground coupled heat pump of 55 kW which during winter time takes heat from the ground, whereas during the summer it rejects the heat absorbed in the building back to the ground in order to avoid the thermal unbalance of the ground. Yet, in summer time too much heat from the building is extracted, so part of this heat is actually extracted outside by an external coil in order not to have the ground too warm at the beginning of heating season. As an auxiliary system is used a boiler of 42 kW and a classic split system cools the package room during summer time.

Monitoring of the building

The monitoring of indoor climate conditions is accomplished by loggers for temperature and relative humidity placed in different places in the building: in offices and a store with packing room. Due to the request there were placed extra loggers in the packing area at different heights in order to evaluate the air stratification and to have a full overview of the climate inside the building.

The time step for logging of data is every 6 minutes and the monitored data are collected by a computer reachable by remote connection for monitoring the system and download of the data.

The AHU 3 is monitored by an internal control system which collects information about temperature, humidity, fans consumption, and air flow rates and pressures, and other parameters.

All collected data can be used to evaluate the effective functioning of the entire system, showing if the solution chosen for this multi-functional building is the optimal solution for energy saving and good IAQ. Also hopefully, this is another step on the way for a greener world.