Monitoring Passive houses China
To describe the contents of this report shortly but thoroughly enough this text about the project, which was presented at the 21. Passive House Conference in Vienna in April 2017, is reproduced here almost completely [Kaufmann 2017]. For figures see the main text.
The Passive House office building and guest house in ZhuoZhou was completed in July 2015. The building was planned and realized by Chinese companies with consulting provided by the Austrian Passive House expert team, Schöberl and Pöll and Passive House Institute (PHI). As the construction had already started when the decision to make the building a Passive House was taken, some details in design could not be fully optimized.
Monitoring of the building started in July 2015. From the available monitoring data after two years of operation, mid of March 2017, the results can be summarized as follows: The building service equipment for cooling and dehumidification in summer and for heating in winter is performing as designed. The users are happy with indoor comfort and the consumption of energy for heating and cooling is a little higher than calculated, but deviations are within reasonable limits and can be explained by user behavior, weather conditions and some planning issues described later in this report.
Just after the beginning of measurements in August 2015 the early data helped to adjust the building services devices and setup parameters: The default settings for cooling and heating power and requirements from the user were discussed in detail and then partly readjusted. Thus the indoor temperatures during the 2nd winter 2016/17 were reduced compared to first winter 2015/16. Average temperatures in the building then were almost everywhere about 22°C. The temperatures in summer 2016 were similarly slightly higher than 2015 but again average temperature was about 25°C and never higher than 26°C.
A very important feature of the building behavior can be seen from the monitoring data, see the graphs in section 2.11 on page 42and following: The electricity consumption of the heat pumps for heating season and cooling season are well separated from each other by a 'neutral' period in spring and autumn with no heating and cooling at all. This validates the findings about thermal behavior of Passive House buildings: as these are very well insulated, air-tight, and ventilation is done with heat recovery, Passive House buildings will only slowly heat up or cool down, so there will never be heating and cooling during the same day. Therefore in spring and autumn, when daily average outside temperatures are within a comfortable range of 20....25°C, a Passive House building will never need any heating or cooling.
The results can be summarized as follows: The overall energy consumption in the office building was about 22 kWh/(m²a) for heating during both winters and about 26 kWh/(m²a) for cooling during summer 2016. In the PHPP calculation the respective limit values for Passive House buildings are 15 kWh/(m²a) for heating and 17 kWh/(m²a) for cooling energy demand. The extra consumption is not at all dramatic, compared to conventional buildings the consumption is very low ─ and what is more, the consumption of the real building can be explained by changing the respective parameters and boundary conditions in PHPP calculation so that the extra consumption can be modelled in PHPP and thus explained reasonably.
The heating energy consumption oft he building can be explained by several reasons:
- Electricity use for office appliances was significantly lower than for typical office use: only 11 kWh/(m²a) instead of typically 30 kWh/m²a, because many office rooms in the building have not yet been occupied up to now. In consequence the overall average internal heat gains including heat from people and electricity were only about 1.8 W/m². Accounting for that in PHPP raises heating energy demand by more than 4 kWh/(m²a).
- Indoor temperatures in most rooms in winter were higher than 20°C. The average in-door temperature in the office building was about 22°C. This raises heating energy demand by about +4 kWh/(m²a)
- The main influence for heating energy consumption comes from longer daily and weekly operation of the ventilation system: so the average air flow in/out was significantly higher than planned as the operation time of the ventilation system (6 a.m. to 21 p.m. thus 15 hours on 7 days a week) was longer than assumed previously. The higher average air flow results in an extra heating energy demand of about 5 kWh/(m²a)
- As the rough concrete construction was designed before the decision about Passive House was taken, the room heights in level 4 were too low to cover the supply air ducts and waste air ducts to connect the ventilation unit to the rooms in building. Therefore these warm air ducts on roof running through outside air are quite long (> 45 m). For this and other reasons the performance parameters of ventilation systems must be assumed to be significantly lower than originally assumed. This raises the heating energy by about 3 kWh/(m²a).
- The monthly average outside temperatures at ZhuoZhou during the time of September 2015 to September 2016 were in all months about 1 to 2 K higher than the previously assumed temperatures coming from reference data set. On the other hand the solar radiation available in winter months (October to March) is significantly lower (winter smog) than those in reference data set. This raises in total the heating energy demand in winter by about 4 kWh/(m²a).
- • The numbers of extra energy demand mentioned above do not sum up linearly. Combining all the mentioned effects it can be explained that heating energy consumption of building in real operation is about 12 kWh/(m²a) higher than the value of the certified Passive House configuration.
- Some of the effects, like the performance of the ventilation system are due to planning issues, which could not be changed as mentioned before. But as a general hint for planning such basic details and features should be considered carefully in further projects.
- On the other hand, most of the mentioned effects result from operational conditions such as weather during these two years. Some of the indoor conditions could be changed by the use of the building. Anyway, the difference between designed values of heating energy demand and actual heating energy consumption is within reasonable limits and not dramatically high and can be accepted and explained within as typical 'user behavior'.
The difference in cooling energy consumption can be explained as follows:
- Shading: If users in building forget to close the shading lamella, this would cause higher solar loads and thus higher cooling energy demand in summer. An additional solar throughput (z-value 60% instead of 20% as assumed in PHPP) would raise cooling energy demand by about 1 kWh/(m²a). The shading is operated in both buildings automatically, so no extra cooling energy because of misalignment of shading.
- The average indoor room temperatures which were chosen by users, were about 24 °C instead of the recommended 25 °C. This results in extra 1,5 kWh/m²a cooling energy demand.
- The higher outside temperatures measured during the two summers raised the cooling energy demand by about 4 kWh/(m²a).
- Solar radiation data from measurements show no higher values than standard weather data set. So this makes no difference.
- Users to open windows manually during daytime in summer can raise the cooling energy consumption as heat and mainly more humidity is entering the building not controlled. Assuming only a small extra air change of 0.3 per hour in PHPP during summer the cooling energy demand raises about 6 kWh/m²a. This assumption is not fully verified, but this behavior is reported from the ZhuoZhou office building and other projects. To avoid this effect, users should be instructed, that the building is equipped with ventilation and Air Conditioning (AC) system, which will only work properly if windows are closed.
The mentioned effects accounted for in PHPP can roughly explain an energy demand for cooling & dehumidification which is compatible to the measured energy consumption: The measured energy consumption for cooling and dehumidification in summer 2016 was 26 kWh/(m²a) instead of the limit value from PHPP, which is 17 kWh/(m²a). So the overall cooling energy consumption of 26 kWh/(m²a) is reasonable anyway, as it is much lower than for typical conventional buildings.
Apart from heating and cooling energy the consumption of electricity for the central ventilation systems shows a specific electric efficiency of 0.76 Wh/m³ for an average air flow of 5000 m³/h (assuming an operation seven days a week from 6 a.m. to 9 p.m.). This might be better for a ventilation design with shorter and wider air ducts and wider air outlets and thus with lower overall pressure losses. But some optimizations as reduction of air flow in normal operation was already done, so that the specific number could be reduced during first year.
Summary and conclusion: Monitoring is necessary to achieve good building performance
Monitoring as done in the ZhuoZhou building was very helpful to identify some problems which frequently come up with new buildings ─ not only in Passive Houses. So doing monitoring together with an extended commissioning and quality control helped to setup the building correctly to get the performance as designed and intended. With that respect a monitoring and a detailed control of any buildings setup should be regarded mandatory.
The monitoring research project was financed by Austrian government [BMVIT 2015]. It was reasonable to understand this first Passive House building in the Hebei region in more detail and what is more to validate the so far theoretical assumptions about Passive House conceptions in a Chinese climate region. Those governmentally financed monitoring studies are therefore really necessary from a scientific point of view, too.
So monitoring is necessary and helpful anyway, but the question is, if data collection needs to be so sophisticated as in research projects like that in ZhuoZhou Passive House building, or if less data would be sufficient as well. Normally an economically reasonable 'building-setup-procedure-monitoring' for the owner and user should just provide sufficient data to figure out possible tasks and actions for optimization. This could be data from the most important energy meters, such as electricity for heat pumps, which should be recorded separately from electricity of all other office appliances and lighting in the building. Furthermore temperatures should be recorded in some rooms and in ventilation system. Last not least indoor air quality in general should be monitored to realize and repair possible malfunctions.
In the end, the monitoring project could prove, that the ZhuoZhou Passive House building does perform as intended and that it can serve as a good example and show case for further development of sustainable buildings in China. The Authors want to thank the owner and wish him and the users many years of good work and life in there.