Monitoring it’s a key topic to understand whether a building is working properly and users behave in the correct way. In order to have some inputs about this topic a lecture from Passive House institute was presented in Darmstadt.
The main questions are: which factors we have to measure to compare calculated data with real building? How to match measured data with real data?
To know if the user behavior in correct, you have to ask directly to the users. That is what Passive House Institute did with two buildings in Darmstadt. They measured and analyzed the data of energy consumption over three years, then asked to people if they’re satisfied, 90% are satisfied and 50% are very satisfied. Survey will be done again in two years. A minimum percentage of unsatisfied people is considered acceptable and inevitable.
When planning a monitoring there are two extreme options: minimal monitoring VS scientific monitoring. You should decide according to what is needed and which are the limitations.
It’ easier to have data on final energy side and is more difficult to have it at the useful energy level. The measurement is done on heat generation, on storage that have some losses and on distribution with losses. If the losses are few the measurement data can be used.
Minimum measurements technology required is manual reading of general meters (heat supply, thermal solar supply, power consumption, water consumption…), minimum 1 per year, best every month.
If you have a gas meter and a heat meter after the boiler you can calculate the efficiency of the boiler. You can add single meter on single flats, so you can know the system losses.
If you need a very detailed monitoring, you can have a single circuit.
In case the heat generator is a heat pump it’s important to know also the cold source temperature.
In efficient building is important to monitor electrical energy consumption, because there are more electrical consumption than heating.
Which are the influencing factors in monitoring?
- Thermal quality building
- User behavior (people, clothing, activity)
- Weather condition
- Function building services
The calculation according to the building codes algorithms are not suitable for comparison with consumption numbers, they are not accurate enough. Demand is different between consumption, to design you should make a calculation more connected with reality (e.g. Passive House Planning Package).
The deviation from law to reality (at least in Germany) is mainly in overestimation of internal gains. With PHPP they measured heating consumption very accurately, with energy losses and gains (solar gains, internal heat gains…).
In high performing buildings there are big difference due to indoor temperature. Typically internal temperature is about 21.5°C (according to past monitoring).
Ventilation can change heating demand; in passive house an air change rate from 0.2 to 0.5 can be a quite big difference (1.5 kWh/m2y).
Summing all the possible influences can up to double the consumption, in theory, but they are not present at the same time.
For hot water there is a big data fluctuation. In single house it’s difficult to predict the user behavior, in many apartment instead it can work because you can do statistics and so you can refer to average values.
At least control should be done permanently (minimum one annual date required). Deviation can be clarified by more accurate monitoring.
Rebound effect and saving potential
In passive houses the user behavior can influence the consumption very much.
In insulated building people use to have higher temperature inside; anyway in high performance houses, even if people don’t behave correctly, the extra consumption is not very high in absolute value, better than in renovated houses (not passive).
The measurement of 32 flats in Hannover (passive houses) shows that some need more heating, some need less, statistics show a typical standard deviation (1,2 kWh7m2y). The average value fits the PHPP calculation.
Measurement accuracy is not better than +/- 3 KWh/m2y.