Water-based Indoor Climate Systems, 2007
www.swegon.com
INDOOR CLIMATE
INDOOR CLIMATE
WHY CREATE A GOOD INDOOR CLIMATE
Experienced indoor climate
Individuals experience the climate as a joint action of several factors that affect our thermal comfort:- Level of activity, the body’s heat production
- Clothing’s thermal resistance
- Ambient air temperature
- Surrounding surfaces’ temperature
- The air’s relative speed
- The air’s relative humidity
According to professor P O Fanger the ideal indoor climate has been attained when people perceive thermal comfort, i.e. when a person is thermally neutral. However, one of the problems you always face when creating a good climate with the help of a climate system is that people perceive the climate differently.
No matter how well you succeed about 5% will still be dissatisfied. The percentage of those dissatisfied will then increase for each degree of deviation from the average person’s most ideal temperature.
Figure 1 shows the percentage of those dissatisfied when the temperature deviates from the average ideal temperature.
Performance levels
What we consider to be the ideal indoor climate is always individual from person to person and studies show that performance levels follow a person's perception. During his time with the research institute, Statens Institut för Byggforskning (SIB), David Wyon undertook a number of studies of people in different work situations.
Figure 2 shows that deviation from the ideal temperature is significant. You can record a reduction in efficiency even after a few degrees of deviation from the ideal. This means it is possible to make a calculation of what an indoor climate investment can mean and in doing so not only is that the perception of comfort now positive but efficient.
Figure 1.Expected percentage of dissatisfied (PPD = Predicted Percentage Dissatisfied) as a function of the thermal comfort perception (PMV = Predicted Mean Vote).
-2 = cold
-1 = slightly cold
±0 = neutral
+1 = slightly warm
+2 = hot
Figure 2.Efficiency as a function of the deviation from the ideal temperature.
Heating and cooling requirement in a standard office
Here follows an example that illustrates the thermal balance in an office. The room has windows with energy glass, U-value approximately 1.3 W/m2, K. Figure 3 shows how the relationship between the heating and cooling requirement changes in the room due to the separate heat sources you normally have in an office today.
The person emits approximately 100 W. When the lighting is switched on a further 120 W is added. When the person, lighting, computer and sun are included the load amounts to approximately 650 W in the room. With an outdoor temperature of –18°C the heating losses through the exterior walls, window, etc. for the room are approximately 180 W to 300 W depending on where the room is located in the building. The higher value relates to a corner room. Accordingly, the room’s cooling requirement is nearly always greater in all instances than the room’s heating requirement even when it is -18°C outside.
Is comfort cooling required to create a good working environment?
Yes, we claim this at Swegon with the following examples.
Conditions: | |
Working environment: | Office |
Performance levels: | 100% up to 25ºC over that a reduction by 10% per ºC |
Building: | Heavy structure with concrete beams and brick facade |
Ventilation with air-based cooling: | 4 l/s m2 operating at night during the summer |
Ventilation with water-based cooling: | 1.5 l/s m2 |
Fan efficiency: | 50% |
Cooling requirement: | 35 W/m2 |
Salary costs: | 350 SEK per hour and employee including lost percentage allowance to cover fixed costs |
Equivalent operating period: | 700 h/year |
Electricity price: | 0.8 SEK/kWh |
Cost as a result of the loss of production
The cost due to loss of production will be 6,160 SEK per year and employee. If each employee takes up 20 m2 incl. secondary areas, this gives a cost of approximately 310 SEK/m2 per year.
This should be set against the investment and the annual operating costs.
The investment cost for the comfort cooling installation
The normal investment cost for the comfort cooling installation incl. room cooling amounts to 700-800 SEK/m2 office area.
Based on relatively simple repayment calculations the repayment period will be about 3 years for the investment in a good indoor climate for the employees.
Operating cost
The additional operating cost for comfort cooling will be approximately 8.60 SEK/m2 year.
The saving for the lower air flow with comfort cooling will be approximately 31 SEK/m2 year. Consequently, the flow reduction by 2.5 l/s m2 reduces the operating cost for the fans so that it covers, by a good margin, the cooling installation’s operating cost.
Figure 3.Thermal balance in a standard office.
A = Sun
B = PC
C = Lighting, 120 W
D = Person, 100 W
E = Transmission