Capstone Efficiency Upgrade: Evaluate and Improve a Household Thermal System

What this capstone is (and what “efficiency upgrade” means at home)

This capstone chapter is about taking one real household thermal system, measuring how it performs today, identifying where performance is being lost, and implementing one or more upgrades that measurably improve it. “Efficiency” here is not a single universal number; it depends on the system. For a water heater it may be energy per liter of hot water delivered at a target temperature. For a space-heating system it may be energy per degree-day of heating delivered. For a refrigerator it may be energy per day at a given internal temperature and usage pattern. The practical goal is to reduce wasted energy while maintaining the service you actually care about: comfort, hot water availability, food safety, drying time, etc.

The key mindset: treat your home system like a machine with inputs, outputs, and losses. You will build a baseline, then change one thing at a time (or at least document changes), and verify improvement with data rather than impressions.

Choose a target system and define the “service” you want

Pick one system that (a) runs often, (b) you can access safely, and (c) you can measure without specialized lab gear. Good candidates:

• Domestic hot water: electric tank, gas tank, or tankless heater
• Clothes dryer (electric or gas)
• Refrigerator/freezer
• Room air conditioner or mini-split heat pump
• Hydronic boiler with radiators (if you can measure fuel and temperatures)

Define the service in a way that is measurable and tied to user experience. Examples:

• Water heater: “Deliver 40 L of 40–42°C shower water with minimal energy.”
• Dryer: “Dry a standardized load to a consistent dryness level.”
• Refrigerator: “Maintain 3–5°C fridge and −18°C freezer with typical door openings.”
• AC: “Hold 24°C indoor temperature at typical occupancy.”

Write down constraints: budget, allowed modifications (renting vs owning), noise limits, and safety constraints.

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Instrumentation: a maker-friendly measurement kit

You can do a strong evaluation with a small set of tools. Use what you have; add only what improves confidence.

Electrical measurements

• Plug-in power meter (for 120 V plug loads): logs kWh, watts, and sometimes power factor
• Clamp meter (for hardwired loads): current measurement; pair with known voltage for approximate power
• Smart plug with energy monitoring (useful for long-term logging)

Temperature and humidity

• Two to four temperature probes (contact or air probes)
• IR thermometer (good for surface comparisons; be cautious with emissivity and shiny surfaces)
• Humidity sensor (critical for dryer and comfort-related HVAC evaluation)

Flow and usage

• Water flow bag test (a bucket + stopwatch) or an inline flow meter for showers
• For gas appliances: utility meter readings over time (or a pulse-output meter if available)

Other helpful items

• Notebook or spreadsheet for a test log
• Painter’s tape and marker to label sensors and test conditions
• Basic hand tools for cleaning coils, replacing filters, sealing gaps

Safety note: do not open sealed refrigeration circuits, gas trains, or electrical panels unless qualified. Many upgrades are external: cleaning, airflow, insulation, control settings, and maintenance.

Build a baseline: measure before you modify

Baseline data is the anchor of the capstone. Without it, you cannot confidently claim improvement. Your baseline should include (1) energy input, (2) delivered service, and (3) conditions that affect performance.

Step-by-step baseline plan (general)

• Step 1: Stabilize conditions. Choose a representative day or repeatable test window. For HVAC, note outdoor temperature; for fridge, keep similar door-opening patterns; for water heater, use a standardized draw.
• Step 2: Log energy. Record kWh (electric) or meter units (gas) over the test period. For cycling devices (fridge/AC), log at least 24 hours.
• Step 3: Log service output. This is system-specific: liters of hot water delivered, pounds of laundry dried, average indoor temperature, fridge internal temperature stability, etc.
• Step 4: Log key temperatures. Inlet/outlet temperatures for water, supply/return air temperatures for HVAC (if accessible), ambient room temperature for a fridge, exhaust temperature and humidity for a dryer.
• Step 5: Document settings and maintenance state. Thermostat setpoints, fridge dial position, filter condition, coil cleanliness, vent routing, tank temperature setting, etc.

A practical baseline is not perfect; it is consistent. Repeatability matters more than fancy sensors.

Turn baseline data into actionable metrics

Choose one primary metric and one or two secondary metrics. The primary metric should match the service definition. Secondary metrics help ensure you didn’t “improve” energy use by reducing service quality.

Examples of primary metrics

• Water heater: kWh per standardized shower (or per liter of delivered mixed water at target temperature)
• Dryer: kWh per load to reach a defined dryness
• Refrigerator: kWh per day while maintaining temperature bounds
• AC/heat pump: kWh per degree-hour of indoor-outdoor temperature difference (a simple normalization)

Secondary metrics

• Time to complete the task (drying time, recovery time after hot water draw)
• Temperature stability (fridge swings, room temperature overshoot)
• Comfort indicators (humidity, drafts, noise)

Simple normalization to reduce “weather noise”

For HVAC, raw kWh/day is misleading because outdoor conditions change. A simple approach is to record average outdoor temperature and compute a “load indicator” like (indoor setpoint − outdoor average) × hours. Then compare kWh per load indicator before/after. It’s not a full building model, but it helps you avoid false wins.

Loss mapping: find where the energy is going

Once you have baseline numbers, do a structured loss mapping. The goal is to identify the biggest, easiest-to-fix losses first.

Loss mapping checklist (applies to many systems)

• Unwanted heat exchange: heat leaking out of hot things (tanks, pipes, ducts) or into cold things (fridge cabinet, cold air leaks)
• Airflow problems: clogged filters, blocked vents, crushed ducts, lint buildup, dirty coils, poor clearance
• Control issues: setpoints too extreme, short cycling, schedules that fight occupancy, sensors in bad locations
• Standby losses: devices consuming power when “idle” (circulation pumps, crankcase heaters, always-on fans)
• User interaction losses: frequent door openings, long hot water runs, overdrying laundry, running exhaust fans unnecessarily

Use your sensors to confirm. For example, a large temperature difference across a blocked filter suggests airflow restriction; a hot compressor area with poor ventilation suggests heat rejection problems; a warm spot on a hot water pipe indicates uninsulated distribution losses.

Upgrade menu: improvements with high payoff and low risk

Pick upgrades that are (1) safe, (2) reversible if needed, and (3) measurable with your baseline metric.

Upgrade category A: Maintenance and airflow (often the biggest win)

• Clean heat-exchanger surfaces. Refrigerator condenser coils, dryer lint paths, AC outdoor coils. Dirt acts like insulation and reduces heat transfer, forcing longer run times.
• Restore designed airflow. Replace or clean HVAC filters, ensure vents are open, remove obstructions around fridge coils, verify dryer vent is not crushed.
• Reduce pressure drop in ducts/vents. Shorten overly long dryer vent runs, remove unnecessary bends, use smooth-wall ducting where allowed.

Measurement idea: for a dryer, compare drying time and kWh/load before and after cleaning lint from the entire path (lint trap housing, blower area if accessible, vent duct). For a fridge, compare kWh/day and compressor duty cycle after coil cleaning and improving clearance.

Upgrade category B: Reduce unwanted heat leaks

• Insulate hot water pipes near the heater. The first few meters often provide disproportionate benefit because they are hottest and lose the most heat.
• Add an insulation blanket to an older electric tank (only if manufacturer guidance allows; keep thermostats and safety labels accessible).
• Seal air leaks around fridge door gaskets (clean gaskets, check for gaps with a paper-strip test; replace if torn).
• Seal and insulate accessible ducts in unconditioned spaces (mastic for leaks; insulation wrap for heat loss/gain).

Measurement idea: for hot water, run a standardized draw and measure how quickly the pipe cools after draw before/after insulation; track kWh/day for the heater if you can isolate it.

Upgrade category C: Control and setpoint optimization

• Adjust setpoints to realistic needs. Lower water heater temperature if safe and acceptable; avoid freezing the fridge colder than necessary; avoid extreme HVAC setpoints.
• Use schedules intelligently. Pre-cool or pre-heat when energy is cheaper (if on time-of-use rates) without increasing total run time.
• Prevent short cycling. For thermostats that allow it, increase minimum run time or adjust deadband to reduce frequent starts.

Measurement idea: compare kWh/day and temperature stability. A setpoint change that saves energy but causes unsafe food temperatures or discomfort is not a real upgrade.

Upgrade category D: Behavior and process changes (free, but must be standardized)

• Dryer: spin clothes longer in the washer; dry similar fabrics together; stop when dry rather than “extra dry.”
• Hot water: lower flow showerhead (while maintaining comfort), shorter showers, fix drips.
• Refrigerator: allow hot food to cool before storing; minimize door-open time; keep reasonable fill level for thermal buffering.

Behavior changes can be real efficiency upgrades, but only if you can keep them consistent and verify service quality.

Capstone project workflow: from audit to verified improvement

Phase 1: Plan the experiment

Create a one-page test plan:

• System chosen and service definition
• Primary metric and secondary metrics
• Instrumentation list and sensor placement sketch
• Baseline duration and sampling interval
• Upgrade(s) to implement (ranked by expected impact and effort)
• Risks and safety notes

Decide your acceptance criteria, e.g., “Reduce kWh/day by 10% while maintaining fridge temperature between 2–5°C.”

Phase 2: Collect baseline data

Run the baseline exactly as planned. If something unusual happens (guests visiting, heat wave, unusual laundry load), write it down. A messy log is better than a clean but fictional one.

Phase 3: Implement one upgrade at a time (when possible)

Single-variable changes make attribution easier. If you must bundle upgrades (e.g., you clean coils and also move the fridge), document both and consider doing an intermediate measurement if time allows.

Phase 4: Re-test under comparable conditions

Repeat the same measurement window and service output. If conditions differ, use your normalization approach and note the differences.

Phase 5: Quantify improvement and check for tradeoffs

Compute percent change in the primary metric and verify secondary metrics stayed within bounds. Also note any new issues: noise, longer recovery time, comfort complaints.

Three worked capstone examples (pick one pattern to follow)

Example 1: Refrigerator efficiency upgrade (kWh/day reduction)

Baseline setup: Plug the fridge into a power meter for 72 hours. Place one temperature sensor in a cup of water in the fridge compartment (reduces short-term swings) and one in the freezer (air). Log room temperature if possible.

• Primary metric: kWh/day
• Secondary: fridge water-cup temperature stays 3–5°C; freezer stays near −18°C (allow some cycling range)

Loss mapping: Check condenser coil condition, clearance behind/under the fridge, door gasket seal, and whether the fridge is near an oven or in direct sun.

Upgrades:

• Vacuum/brush condenser coils and the compressor area (unplug first)
• Increase clearance for airflow (follow manufacturer minimums)
• Clean gaskets; adjust door alignment if it doesn’t self-close
• Set temperature to a measured target instead of a dial guess

Re-test: Repeat 72-hour logging. Compare kWh/day and temperature stability. If kWh/day drops but temperatures rise above safe bounds, adjust setpoint and re-test.

Example 2: Electric water heater upgrade (standby + distribution losses)

Baseline setup: If the heater is on a dedicated circuit and accessible, measure energy over 24–72 hours with a suitable meter (or use utility interval data if available). Also do a standardized draw test: run hot water at a fixed flow for a fixed time, record inlet cold water temperature (approximate), and record delivered mixed water temperature at the shower or faucet.

• Primary metric: kWh/day (for whole heater) and/or kWh per standardized draw
• Secondary: delivered hot water meets comfort requirement; recovery time acceptable

Loss mapping: Feel for hot spots on nearby pipes, check if hot water lines run through cold spaces, note tank setpoint, and listen for frequent reheating cycles when no one uses hot water (standby).

Upgrades:

• Insulate the first 2–3 m of hot water pipe (and cold inlet if condensation is an issue)
• Lower tank setpoint modestly if safe for your household and local guidance (especially if you have mixing valves)
• Fix hot water leaks and dripping fixtures
• Add a timer control only if it matches your usage pattern (verify it doesn’t cause longer reheats that negate savings)

Re-test: Repeat kWh/day measurement and the standardized draw. Watch for unintended effects: running out of hot water sooner, or longer recovery that changes behavior.

Example 3: Clothes dryer upgrade (airflow + moisture removal)

Baseline setup: Use a plug-in power meter (electric dryer) or measure gas usage over repeated loads (gas dryer is harder but still possible with meter reads). Standardize the load: same fabric type, similar mass, same washer spin setting. Measure initial load mass (optional) and record drying time to a consistent dryness endpoint.

• Primary metric: kWh/load (or gas units/load)
• Secondary: drying time; no overheating; clothes not overdried

Loss mapping: Check lint trap, lint trap housing, vent duct length and bends, outside vent flap operation, and whether the dryer is pulling makeup air from a tight space.

Upgrades:

• Deep-clean lint path (lint trap area, duct, exterior vent)
• Shorten and straighten vent run where possible; replace crushed flex duct with smooth rigid duct (where allowed)
• Increase washer spin speed to reduce initial moisture (process change)

Re-test: Repeat the same standardized load. A good upgrade often reduces both drying time and energy per load.

Data handling: a simple template you can copy

Use a table or spreadsheet with consistent columns. Here is a compact structure:

Test ID: ______________________   Date range: ______________________  System: ______________________  Upgrade state: Baseline / After Upgrade #___  Primary metric: ______________________  Secondary limits: ______________________  Notes: ______________________  Time stamp | Energy reading (kWh or meter units) | Device state (on/off if known) | Key temp #1 | Key temp #2 | Ambient temp | Humidity | Service counter (loads, liters, door opens) | Comments

For devices that cycle, you can also compute duty cycle from power logs (time above a threshold wattage). Duty cycle is a useful secondary indicator even if you don’t compute detailed thermodynamic performance.

Verification: avoid common capstone pitfalls

Confusing reduced service with improved efficiency

If you lower a fridge setpoint too much, energy rises; if you raise it too much, energy falls but food safety suffers. Always enforce secondary limits.

Changing multiple variables unknowingly

Examples: cleaning coils and also moving the fridge away from a warm wall; changing thermostat schedule while also sealing ducts. Document everything and, when possible, separate changes.

Too-short measurement windows

Many thermal systems have long time constants. A 2-hour test can be dominated by startup behavior. Prefer 24–72 hours for cycling appliances and at least several repeated trials for batch processes like drying.

Sensor placement errors

A fridge air sensor near the vent can read colder than the average food temperature. Use a water-cup sensor for the fridge compartment. For HVAC supply air, avoid placing sensors where they see radiant effects from hot metal or sunlight.

Deliverables for your capstone submission (what to produce)

To complete the capstone in a maker-style, produce:

• A one-page system diagram (hand sketch is fine) showing where you measured energy and temperatures
• Baseline dataset and after-upgrade dataset (raw logs or summarized tables)
• Primary metric comparison with percent change
• Secondary metric check (temperature bounds, time, comfort)
• Photos of the upgrade (cleaned coil, insulated pipe, sealed duct, vent reroute) if applicable
• A short “lessons learned” section focused on measurement and iteration (not a general conclusion)

This structure forces the same discipline used in real machine efficiency work: define the service, measure honestly, change one thing, and verify the result.