Enter RuralHomeSoft™?

RuralHomeSoft (RHS) is a multifunctional home management system based on the popular Phidget (www.phidgets.com) USB interface devices. Its functions are described in the next subsections.

 

Irrigation Controller

• timer, depth and/or evapotranspiration based irrigation schedules
• up to eight microclimate controlled zones
• temperature, humidity, rain sensor and rain gauge input
• optional internet based weather input
• water usage recording , and
• blackout schedules for municipal bylaws

RHS was first implemented as an irrigation management and control system for an array of eight gardens with very different microclimates. In a rural setting when the domestic water source is a limited flow well, it can be a challenge to meet irrigation needs. In addition, well water quality (very hard water) often requires the ratio of well water to natural rainfall be kept to a minimum.

Water needs of vegetation - referred to as evapotranspiration - must be met by a combination of rainfall and irrigation. The term evapotranspiration is derived from: evaporation (water leaving the ground’s exposed surface) and transpiration (water leaving the plant’s exposed surfaces). An ideal situation is achieved when the amount of water applied equals the total evapotranspiration during a daily period. While “ideal” is not really achievable given the number of variables involved, a workable compromise is feasible. This involves complex computations based on soil type, weather, and so on. If computed water demand exceeds rainfall, irrigation must be applied to make up the difference in the most effective manner. RHS provides a means of entering detailed landscape information for up to eight garden zones. This information is used to calculate daily water demand for the associated vegetation. With this information, and the amount of rainfall, daily irrigation needs are determined.

 

Figure 1: Landscape zone descriptions

Figure 2: Zone soil characteristics

However, measuring the true contribution of rainfall is a challenge. Soil type, landscape contour and garden canopy all impact the percentage of rainfall actually reaching the plant’s roots where it is needed. RHS can accept data from a local rain gauge or, alternatively, from an internet weather station. Additional data such as temperature, humidity and wind speed are obtained from a combination of online data and local sensors. Once the total amount of water needed is calculated and rainfall is taken into consideration, irrigation can be applied using one of three methods: timed, fixed depth of coverage, or measured coverage. The latter is the most efficient. Zones can be irrigated in sequence to prevent stress on a well and in short intervals to reduce waste due to runoff. If a municipal water source is used, blackout periods can be set up to respect local bylaws.

Figure 3: Zone timer/irrigation strategy setup

 

HVAC system monitoring

• logging of activity for up to three stages
• monitoring and recording of heat pump loop temperatures, and
• realtime graphing of stage activity and loop temperatures

We recently had a closed loop two stage geothermal heat pump with electrical resistance backup heater installed. Comparing actual capital and operating costs to those used for economic justification was of interest. Therefore, RHS was modified to capture information on cycle run times for the heat pump and the electric backup heater. There are two configurations for ground source heat pumps: closed loop and open loop. Performance of heat pumps is affected by the temperature differential between the source (ground) and sink (forced air, in-floor). An empirical relationship exists between the source temperature and the performance rating of the heat pump (within a reasonable range of accuracy). To estimate the performance, RHS captures heat exchanger input and output temperatures with temperature sensors attached to the loop pipes. Installation of current detectors (described in the next sub-section) for the heat pump and domestic hot water in the electrical panel, provides the additional information required to assess system economics. Records for previous heating seasons provide data for a cost comparison.

 

Figure 4: Real time HVAC cycle graph

 

Power usage monitoring system

• logging of power usage on two independent circuits
• realtime graphing of voltage, current and kWh usage

This feature was referred to in the HVAC section. RHS can capture power usage for two cirucits as well as voltage level. The choice of circuits to measure depends on what information is important at the time. In the case of our heat pump, the circuits chosen are the heat pump and the domestic water heater. The water heater was chosen because the heat pump is fitted with a de-superheater. The latter preheats water in a separate tank prior to final heating in a regular hot water tank. Our economic comparison will be made between household hot water/heating using propane and the heat pump/electric hot water scenarios. While the wintertime water heating is not “free”, the summertime heating essentially is. For summertime, power measurement circuits will be switched to a pool heat pump and water well pump.

 

Figure 5: Real time total kWh usage graph

 

Figure 6: Real time voltage level graph

 

Other RHS functions

• Cold cellar heater controller
• Basement dehumidifier controller

One’s wishlist for home management system functionality can be long. Keeping it to a practical level is always the challenge. Two additional problems faced us due to sub-zero winters and hot humid summers: plummeting cold cellar temperatures and soaring basement humidity. RHS is now used to address both of these problems. While not in the publicly available version of RHS, the author’s version has two additional features:

• Measuring sump pump flow, and
• Turning outside lighting on and off at sunset/sunrise

 

System activity reporting

• graphs and tables of events and activities for all of the above functions, and
• daily emails with summary reports of key system information

The advantage of using a computer for home automation is the ability to capture data for future analysis and comparison purposes. RHS is no exception in this respect. The richness of the data, of course, depends on the number of sensors installed. Sensor readings are stored at predefined intervals (such as temperature/humidity/voltage) or when real time events occur (such as heat pump stage on/off cycles).

Figure 7: Net daily irrigation

 

Finally

Home automation means different things to different folks and the methodologies for achieving the end result vary considerably. RHS was created to meet the author’s specific needs and has been successful in doing so. There may be aspects of this system others can use in their personal circumstances. The software has, therefore, been made available at no charge on the author’s web site: www.peterphrastus.com. Instructions for implementing a sample system are provided along with some sources for hardware components. Enjoy!