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===== Monitoring of the "Good Energy House", Minneapolis, Minnesota, USA =====

Authors: Tim Eian (TE Studio, Minneapolis) and Søren Peper (Passivhaus Institut)

===== Introduction =====

The single-family house in Minnesota, USA, was designed as a Passive House and residents moved into it in 2020. So far it has been occupied by four people and is heated and cooled monovalently with a heat pump. A second heat pump is used for domestic hot water supply with ‘ambient air’ as the heat source. This building is suitable for a more exact investigation of the consumption values due to its being well-equipped with measurement technology for the different electricity loads and the indoor air conditions, as well as the prepared PHPP energy balance.

[{{:picopen:monitor_1.png?550 |Fotos: Corey Gaffer, Gaffer Photography}}]

===== Introducing the building =====

Designed by TE Studio founder Tim Delhey Eian (Dipl.-Ing., CPHD p3829) as a home for his family, the Good Energy House was built in 2019/20 and serves as a beacon for sustainability, as well as a best practice example for the design firm and its partners. The 197 m² large house is exemplary for modern, sustainable and carbon neutral living in Minneapolis, Minnesota.

Tim Delhey Eian is the founder of Passive House Minnesota, which is part of the Passive House Network. The Passive House Network is an affiliate of the International Passive House Association (iPHA).

[{{ :picopen:monitor_2.png?600 |Pictures: Tim Eian/ TE Studio}}]



===== Impressions from the construction period 2019/2020 =====

In total, the house offers about 197 m² of living space on two floors and a 60 m² large adjacent climate-controlled garage. Both the front and back yards have generous covered outdoor spaces for enjoyment, entertaining, projects, and to keep snow and debris out of the barrier-free ground-level entrances. The ground floor has been designed keeping growing old in mind.

{{ :picopen:monitor_3.png?600 |}}

===== Layout of the ground and upper floors =====

The ground floor of the Good Energy House is barrier-free and offers an open-plan living area, a kitchen, a storage room with access to the attached 2.5-car garage, a guest room/home office and a ¾ bathroom. On the second floor, there are two smaller bedrooms with a shared bathroom. A generous hallway connects a vertical space near the stairs with an interior balcony overlooking the living room on the ground floor. A centrally located laundry room, which also serves as a storage room, is located on the north side of this floor. The master suite completes the floor plan on the west side with a generous bedroom, a walk-in closet and a bathroom.

[{{ :picopen:monitor_4.png?600 |Ground floor with living/dining area. Pictures: Corey Gaffer, Gaffer Photography}}]
[{{ :picopen:monitor_5.png?600 |Staircase to the upper floor and indoor balcony seating area on the upper floor. Pictures: Corey Gaffer, Gaffer Photography}}]


The design is simple and well-proportioned, with an emphasis on function and providing adequate space without being overly large. From cork floors to reclaimed ash wood ceilings and stairs, the materials and surfaces were chosen taking into consideration their impact on the environment and people. The home's exterior is durable, with metal panels installed where the house is difficult to reach for maintenance, and locally-sourced rough-sawn cedar within arm's reach for later upkeep.

The windows were sourced from Germany, which is typical for Passive House projects in cold climates in the US, as they offer quality and performance in Central Europe that has not yet been matched by locally manufactured products at the time of this writing. The windows facing east, west and south have motorised external blinds for sun protection.

[{{ :picopen:monitor_6.png?600 |Upstairs bedroom and downstairs kitchen. Pictures: Corey Gaffer, Gaffer Photography}}]


The house is built as a timber frame construction with supports at a distance of 61cm (two feet) to reduce the structural wood proportion and optimise insulation values. The double/cavity wall is about 51 cm thick from the inside to the outside and is filled with compressed cellulose insulation. All of the wall cladding is ventilated. The building foundation consists of insulated concrete formwork blocks installed at a frost depth of approximately 1.10 m below grade, set on fully insulated strip footings. The roof has a slight slope and is covered with EPDM roofing membrane. Downpipes are directed into a garden area on the site, so that almost 100% of the rainwater seeps into the ground on the premises.

The building envelope plays the biggest role in keeping the interior at room temperature. The mechanical ‘backup’ system consists of an outside air heat pump for the house and garage and a dehumidifier for the house. Ventilation of the house takes place by means of a central ventilation system with heat and energy recovery for the entire house. Domestic hot water is provided by an air-to-water heat pump (DHW-HP) and stored in a tank. The use of a shower water heat recovery pipe simplifies hot water generation. It uses the energy of the wastewater from the shower, washbasin and laundry room on the upper floor. The external blinds are controlled by a building automation system that also ensures temperature and humidity control as well as other comfort-relevant features.

===== Specific values, technology and certification =====

  * Certified Passive House Plus (Project ID 5894)
  * HERS score: -8
  * EPA WaterSense compliant
  * Highly insulated, airtight building envelope (n50 = 0.22 h-1)
  * Passive House windows with triple glazing and fully automatic motorised external shading
  * Thermal bridge free details and construction
  * Central ventilation system with enthalpy heat recovery
  * Electric air-to-air heat pump system for heating and cooling with dehumidification (house: Mitsubishi SVZ-KP12NA with EH05-SVZ-S (3.5/ 5kW), garage: Mitsubishi MSZ-GL09NA (2.6kW), outdoor unit: Mitsubishi MXZ-2C20NAHZ2 (5.9kW), dehumidifier: Therma-Stor Ultra-Aire 70H)
  * Water heating: electric air-to-water heat pump (brand: Rheem Professional Prestige Hybrid, model: PROPH50 T2 RH350 DCB (2020), tank size: 190 litres, power: 1.23 kW (compressor), noise: 49 db(A), preset tank temperature: 120 ºF /48.9 ºC)
  * Wastewater heat recovery unit (brand: RenewABILITY Energy PowerPipe, model: R3-72, diameter: 89 mm, length: 1.829 mm, efficiency: 58.9%
  * Heat-insulated hot water pipes all throughout the house
  * LED lighting in the entire building
  * 12 kWp photovoltaic system on the roof; grid-connected (100% wind and solar power)
  * Wallbox for electric vehicles in the adjacent garage
  * Barrier-free design and accessibility of the ground floor, ground-level entrances

===== Monitoring 2023 =====

The measurement data of the building for a whole year was evaluated by the Passive House Institute. The entirely electrically supplied building is heated and cooled by means of a multi-split heat pump, as mentioned above. This heat pump also supplies the garage (approx. 60 m²) connected with the house. Another heat pump is used for hot water generation (hot water heat pump). The heat source for the hot water heat pump is the room air, which accordingly has to be additionally heated during the heating period. With this kind of supply, the final energy consumption can be recorded with just two electricity meters for both heat pumps. However, intermediate steps are still necessary for evaluation of the results for the purpose of checking performance.

==== Electricity consumption ====

The electricity consumption values for 2023 (1 January to 31 December 2023) will be evaluated. The electricity consumption of the individual consumers in the building was measured in great detail. The evaluation shows that in the PHPP calculation tool, the estimated values for individual consumers such as the cooker, dishwasher, washing machine, etc. correspond very well with the consumption values. Only the consumption of IT equipment and other small consumers (sockets, light, etc.) is underestimated in the PHPP. This is probably due to the fact that the users are working from home 100% of the time.

For the further analysis of electricity consumption, the consumption of the multi-split heat pump (heating/cooling) had to be split between the house and the garage. This was done with the help of the PHPP calculations for both buildings. For 2023, the result is divided into 60% for the house and 40% for the garage. Depending on the weather conditions, this distribution will be slightly different each year. It should be noted that the garage is kept at 10ºC in winter (‘frost-free plus’), and thus does not have normal room temperatures like the house.

After dividing the electricity consumption values between the house and garage, it can be seen that a total amount of just 12.4 kWh/(m²a) of electricity was used for the entire heating and cooling of the house (without the garage) each year. This demonstrates the success of the efficient building with a heat pump. Only 4.1 kWh/(m²a) of electricity was required by the hot water heat pump for hot water generation. For this measurement, extraction of heat from the room air for hot water generation is included in the 12.4 kWh/(m²a). The figure below provides an overview of the distribution of the total electricity consumption:


{{ :picopen:gemessener_stromverbrauch_2023_1.png?600 |}}

A total of 65% of electricity is consumed in the residential building and 35% is used for the garage, including charging of the two electric cars. The PV system generated as much electricity in 2023 as the amount consumed in the house, i.e. excluding the garage and car charging (PV generation 11.409 kWh/a, building consumption 11.035 kWh/a). Of course, electricity generation by the PV system is characterised by the typical summer peak and a winter low. Directly offsetting generation and consumption would disregard the question of long-term seasonal storage.

==== PHPP balance for the heating demand ====

If one considers the calculated heating demand of the building according to the PHPP, the significant influence of the actual internal heat sources (electricity consumption, people) and the actual weather as well as the actual room temperature becomes apparent. According to the PHPP, with the usual standardised approaches (average Minneapolis weather, 20 °C indoor temperature in winter), the house has a heating demand of 14.2 kWh/(m²a) (PHPP calculation for the certification). If the actual electricity consumption and weather in 2023 are taken into account, the heating demand drops to just 6.2 kWh/(m²a). If one then takes into account the measured room temperature of 21.5 °C in winter, this increases slightly to 8.3 kWh/(m²a). This is the order of magnitude that can be expected for the measurement of consumption. It should be taken into that an accuracy of ± 3 kWh/(m²a) can be assumed for calculating the balance. The large relative influence of the boundary conditions is typical for such energy-efficient buildings.


{{ :picopen:phpp_2.png?600 |}}

==== Heat consumption ====

A comparison between the heating demand from the PHPP energy balance and the measurement of the actual consumption is now of interest. In order to obtain a measured value that can be meaningfully compared with the PHPP result, a few additional steps are necessary. This procedure is outlined in the illustration.

[{{ :picopen:ablaufschema-engl_3.png?600 |Schematic representation of the data evaluation process for ‘heating energy’.}}]

First of all, the electricity consumption must be divided between ‘heating’ (winter) and ‘cooling’ (summer). In the next step, it is necessary to divide the electricity consumption of the multi-split heat pump between the two parts of the building with the help of a PHPP calculation for the residential building and another PHPP calculation for the garage. For this, the two PHPP calculations must be updated with the measured room temperatures, the weather conditions during the evaluation period (2023) and the measured domestic electricity consumption (IHG). With this information, the electricity consumption of the heat pump for space heating of the house can then be determined.

The heating energy consumption of the building is calculated from the electricity consumption for heating based on the coefficient of performance of the heat pump. The coefficient of performance of the heat pump was not metrologically determined. This field measurement would have involved a lot of effort, therefore only the information provided by the manufacturer was available, which was used here. Since this information (laboratory values) are not always identical to the performance during normal use, in addition a reduced value for a potential range is applied (75%). A heating demand of 16.5 to 22.0 kWh/(m²a) results for the building from these measured values.

This heating energy consumption also includes extraction of the heat from the room air by the hot water heat pump. The distinction between space heating and heat extraction by the hot water heat pump is only made explicitly when calculating the demand using the PHPP.

Accordingly, the value of 16.5 to 22.0 kWh/(m²a) includes about 7.6 kWh/(m²a) heat extraction by the hot water heat pump. Consequently, without the influence of the hot water heat pump, about 9 to 14.5 kWh/(m²a) remain for space heating. Thus a very good result is achieved, even with the slightly higher indoor temperature (21.5°C).

Taking into account the accuracy of the somewhat complicated balance calculation (PHPP) and the accuracy of the measurement including the distribution of consumption across the various uses, there is a convincing correlation between the measured values and the PHPP calculation.

{{ :picopen:heating_4.png?600 |}}

==== Cooling energy ====

For calculating and measuring the necessary cooling energy, the same procedure was that for heating was used. From the electricity consumption during the summer period using the coefficient of performance of 3.2 for cooling or 2.6 when reduced (75%), the measured cooling energy results as 16.1 to 21.5 kWh/(m²a). This means that for cooling in this climate, this energy-efficient building consumes exactly the same amount of energy as it does for heating.

To illustrate the achievable accuracy, the illustration additionally shows the extent of the influence of external shading of the building (‘PHPP without shading’). It is therefore crucial to use shading devices meaningfully in order to manage with only a small cooling output. This analysis shows that in this building, the shading with automatic control is used appropriately in a target-oriented way. According to the PHPP, for the information relating to the cooling demand the heat extraction of the hot water heat pump (2.7 kWh/(m²a)) in summer must also be taken into account as this contributes to heat extraction (cooling).

Overall, there is also a fairly good correlation between the PHPP balance calculation and the measured values also for cooling.

{{ :picopen:cooling_5.png?600 |}}

===== Experience gained with operation and improvements during the first few years =====

A water heater with an air-water heat pump (DHW-HP) is used, which is connected to a shower water heat recovery system. This heat recovery system uses the residual heat remaining of the wastewater from the bathroom on the upper floor. This preheats the fresh water entering the cold water inlet of the water heater. In this way, the energy consumption of the water heater is considerably reduced. Both devices are located on the ground floor in the storage room between the garage and the kitchen. It should be kept in mind that the manufacturer of the hot water heat pump stipulates a minimum room size of about 7 m² for the hot water heater. Since the device draws warm indoor air from the surrounding space to generate hot water, this is meant to prevent excessive cooling of the room air (heat source).

This hot water heat pump has proved highly effective for a family of four, although it is the smallest size available. Sufficient hot water was always available. The device is usually operated in the ‘heat pump only’ or ‘energy efficiency’ mode.

==== Energy consumption ====

In the last four years, the hot water heater has consumed an average of 766 kWh of electricity per year, which is about 2.1 kWh per day. It should be noted that the building is located in a very cold climate zone and that in winter the tap water reaches the building at a much lower temperature than it does in the summer.

==== Experience ====

With increased use of hot water (showering, laundry), the operating time of the hot water heat pump is correspondingly long. The two most noticeable effects of this device in the immediate vicinity of the living spaces are the noticeable noise emission and the cold extract air. The unit is quite noisy. As an indication, the noise level is somewhere between that of a fan and a vacuum cleaner. The unit has to draw in the room air and then pass it through the heat pump, where the heat is extracted from it. From there, the air is returned to the room. The extract air temperature can be a minimum of 9 ºC [48 ºF]. The power consumption in heat pump mode is just under 400 W. The electric power when the electric post-heater is in operation can exceed 5 kW (however, the device is never operated in this way). It is possible to set up the unit in such a way that only the electrical supplementary heating is used, which would make operation virtually noiseless. However, the energy consumption would be correspondingly much higher.

==== Modifications and improvements ====

The unit was operated with its standard configuration for a year. Measures were then taken to reduce the noise level: a 45º foam material elbow left over from the ventilation system installation was affixed to the extract air opening and a silencer was mounted on the air inlet (see picture). With this combination, a noise reduction of almost 50% was measured at a distance of about 3 m. This setup has been kept in place ever since.

[{{ :picopen:monitor_12.png?600 |Air-water heat pump (DHW-HP). For optimisation, retrofitting with 45º foam elbow at the exhaust air opening (bottom) and intake manifold with pipe silencer (top). Pictures: Tim Eian/ TE Studio}}]

The cold extract air from the unit flows from the installation room through the living room. This was perceived as particularly disturbing in winter. After about three years of operation, an improvement was therefore sought. The central ventilation system is used for the entire house. This system is controlled by an intelligent home automation system that processes several inputs from sensors and other devices. The extract air opening of the hot water heat pump was equipped with a temperature probe and the ventilation system was set up so that it always circulates air when the extract air temperature of the water heater is below 17 °C. In summer, this means that the cooled and dehumidified extract air from the water heater is circulated throughout the house to achieve ‘free’ air conditioning and dehumidification. In winter, this recirculation of the indoor air ‘sucks in’ cold extract air and conducts more warm air into the storage room and thus to the hot water heat pump. This shortens the operating time of the hot water HP and the cold air from the hot water HP is distributed throughout the house more quickly.

When the heat pump system (heating) of the house is heating actively, the extract air from the storage room (where the hot water HP is installed) is also routed through the heat pump via a ventilation grille in the storage room and thus immediately reheated to room temperature. This significantly reduces the effects of the cold extract air from the hot water HP.

===== Summary and conclusion =====

In summary, it can be reported that this system works well and is likely to be perfectly acceptable to most Americans – even without the improvements that were made. For optimisation in a further construction project, the water heater would be placed further away from the living area. Since the building has neither a basement nor a utility room, such a solution was not feasible here. It is also conceivable to install the appliance in a separate laundry room. This room is usually warm and humid due to the washing machine and heat pump clothes dryer, so the air-to-water heat pump water heater could benefit from these conditions. Noise and temperature fluctuations will be more likely to be tolerated in a separate laundry room. In a conventional house with a utility room, the unit can also be easily installed together with other mechanical devices and away from living spaces.

It must be pointed out that in a timber frame construction (as is common in the USA), installing a hot water heat pump on the upper floor could cause vibrations and noise in the timber frame floor system. This consideration led to the water heater being left on the ground floor instead of being installed in the laundry room on the upper floor.

===== See also =====

Tool: [[:planning:tools|]]

[[:sinfonia:monitoring_heat_consumption:calculation_and_demand|]]

[[:phi_publications:nr.45_monitoring_consumption_minimal_monitoring|]]