Monday, 26 May 2025

Energy Efficiency in Housing - 'this is a personal look into this subject.'


 

Here are several of the most efficient, low‐pollution ways to generate useful heat without producing chemical toxins—and without gobbling huge amounts of primary energy:


1. Electric Heat Pumps

How they work:

  • A heat pump extracts heat from a low‑temperature source (outside air, ground, or water) and “pumps” it to a higher‑temperature space (your home).

  • Because it moves existing heat rather than creating it by burning fuel, it can deliver 2–5 kWh of heat for every 1 kWh of electricity consumed (coefficients of performance, COP, of 2–5).

Why it’s good:

  • Zero on‑site emissions (if your grid is renewable, it’s effectively carbon‑free).

  • Extremely efficient—often the cheapest heat per kWh you’ll find.

  • No combustion, so no particulate or chemical by‑products indoors.

Considerations:

  • Performance drops in very cold climates (but modern cold‑climate heat pumps mitigate this).

  • Requires electricity; best paired with solar or wind generation.


2. Solar Thermal Collectors

How they work:

  • Flat‑plate or evacuated‑tube collectors absorb sunlight to heat a circulating fluid (water or glycol).

  • That heat can be stored in an insulated tank or used directly for space heating or domestic hot water.

Why it’s good:

  • Direct conversion of sunlight to heat—no combustion and no moving parts (in simplest systems).

  • With good design, solar fraction (the % of your load met by solar) can exceed 50–70% in many regions.

  • System lifetime often 20–30 years with minimal maintenance.

Considerations:

  • Requires roof or ground area with good sun exposure.

  • Needs backup when solar insolation is low (winter, cloudy days)—often paired with a small electric boost.


3. Ground‐Source (“Geothermal”) Heat Pumps

How they work:

  • A loop of buried piping exchanges heat with relatively stable ground temperatures (~10–15 °C).

  • Acts like an air‑source heat pump but with higher and more consistent COPs (often 4–6).

Why it’s good:

  • Very high efficiency year‑round, because ground temperatures don’t fluctuate like air.

  • Quiet, long‑lived, and maintenance‑light.

Considerations:

  • Higher upfront costs due to trenching or drilling.

  • Best for new builds or major retrofits where you can install ground loops.


4. Passive Solar Design & Thermal Mass

How it works:

  • Orient and treat a building to maximize winter solar gain (large south‑facing windows in the southern hemisphere) and thermal mass (concrete, brick, or stone floors/walls) to store heat.

  • Combine with high insulation and airtightness.

Why it’s good:

  • Requires no active equipment to generate heat—nature does it for you.

  • Very low ongoing energy needs if properly designed.

Considerations:

  • Most effective in new construction or major renovation.

  • Requires careful climate‑specific design (overheating risk in summer must be managed).


5. Low‐Grade Waste Heat Recovery

How it works:

  • Capture “waste” heat from refrigeration, data centers, or industrial processes via a heat exchanger and redirect it to space or water heating.

Why it’s good:

  • You’re repurposing heat that would otherwise be dumped to the environment.

  • No new primary energy needed beyond what’s already running the original process.

Considerations:

  • Feasibility depends on proximity of heat source to heat demand.

  • Typically more applicable in commercial or industrial settings.


6. Frictional or Resistive Heating (in small‑scale applications)

How they work:

  • Resistive electric heaters convert 100% of electrical energy into heat; no by‑products beyond wherever the electricity came from.

  • Frictional heating (e.g., induction cooktops) can be very efficient at a small scale.

Why they’re good:

  • Simple, reliable, minimal maintenance.

  • If powered by renewables, effectively zero‐polluting.

Considerations:

  • In large spaces, resistive heating can be more expensive than heat pumps (COP = 1 vs > 2).

  • Best for spot heating or small installations.


Putting It All Together

  1. Minimize demand first: Insulate walls/roof/floor; seal drafts; install high‑performance glazing.

  2. Choose the right technology:

    • If you have good solar access, combine solar thermal + heat pump for backup.

    • In temperate climates, an air‑ or ground‑source heat pump often wins on cost and efficiency.

    • In large buildings or industrial parks, recover waste heat wherever possible.

  3. Integrate renewables: Pair your electric system with rooftop PV or a community wind project so the electricity driving your heat pumps or resistance heaters is truly clean.

By focusing on moving heat (heat pumps), capturing free heat (solar/ground/waste), and dramatically cutting losses (insulation, passive design), you can achieve comfortable warmth with minimal environmental impact—and without creating any chemical toxins or burning fuels.

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With a small, tightly‑sealed, highly‑insulated home the heating and cooling picture looks very favorable:


1. Dramatically Reduced Heating & Cooling Loads

  • Low Heat Loss in Winter:

    • Super‑insulated walls, roof and floor, plus double‑glazed windows and airtight construction, mean heat loss rates can be as low as 1–2 W/m²·K (compared to 5–8 W/m²·K in a typical new home).

    • In practice you’ll only need on the order of 10–20 W per square meter of space to maintain a comfortable 20 °C indoor temperature when it’s –5 °C outside.

  • Low Heat Gain in Summer:

    • Thick doors and well‑insulated walls slow solar and ambient heat ingress.

    • With good shading or overhangs, you’ll cut peak cooling loads enormously—often below 10 W/m²

Result: your annual heating or cooling energy can be reduced by 60–80% compared to a standard code‑built home.


2. Ideal for Small-Scale Heat Pumps & Ventilation

  • Right‑Sized Heat Pump:

    • Because your peak load is tiny, you can install a small ductless (mini‑split) or compact air‑to‑air heat pump—often under 2 kW capacity—for both heating and cooling.

    • Even a single head unit can comfortably handle the whole house, with a coefficient of performance (COP) above 3 in heating and an energy efficiency ratio (EER) around 10 in cooling.

  • Balanced Ventilation with Heat Recovery (MVHR/HRV):

    • In a super‑tight envelope you must bring in fresh air. A Mechanical Ventilation with Heat Recovery system will exchange stale indoor air for fresh outdoor air, while transferring ~80–90% of the heat (in winter) or “coolth” (in summer) between the two airstreams.

    • This keeps indoor air quality high without unduly increasing your heating/cooling load.


3. Excellent Comfort & Control

  • Stable Temperatures: High thermal mass (if you include it) plus thick insulation means indoor temperatures drift very slowly, avoiding cold or hot “spikes.”

  • Zonal Control: In a small house you can easily create one or two heating zones, letting you tailor temperatures room‑by‑room and save even more energy.

  • Humidity Management: The ventilation system can include moisture recovery or dehumidification, keeping summer humidity comfortable and preventing winter dryness.


4. Minimal Operating Costs

  • Very Low Energy Bills: Heating and cooling demand might only be 2–4 kWh/m² annually. For a 100 m² home that’s 200–400 kWh/year—often less than $100 AUD at typical electricity rates.

  • Simple Maintenance: Ductless heat pumps require an annual filter check and occasional service; MVHR units need filter swaps every 6–12 months. No boilers, no chimneys, no fuel deliveries.


5. Key Design & Operational Tips

  1. Ventilation First: Ensure your MVHR is properly commissioned—balance flow rates, seal ducts, and position inlets/exhausts to avoid short‑circuiting.

  2. Passive Solar & Shading:

    • South‑facing glazing (in Melbourne) to capture winter sun.

    • Adjustable external shading (eaves, louvers) to block high summer sun.

  3. Thermal Mass Where Feasible: Materials like concrete slab, brick or tile floors can buffer temperature swings—especially helpful in small volumes.

  4. Smart Controls: A simple thermostat plus occupancy or setback programming can shave off another 10–15% of energy use.


Bottom Line:
A small, super‑insulated, ultra‑airtight house with double glazing and thick doors transforms heating and cooling from a major energy drain into a trivial utility cost. You’ll be able to maintain year‑round comfort with a tiny heat‑pump system and balanced ventilation, enjoy excellent indoor air quality, and pay almost nothing to stay warm in winter or cool in summer.

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If your priority is minimizing heating / cooling loads (and building costs, material use, etc.), the 6 m × 6 m footprint will always outperform the 7 m × 7 m footprint—here’s why:

Metric6 × 6 (36 m²)7 × 7 (49 m²)
Floor Area36 m²49 m²
Perimeter (heat‑loss edge)24 m28 m
P/A Ratio (m per m²)24/36 ≈ 0.6728/49 ≈ 0.57
  • Perimeter/Area ratio: Higher is worse (more exterior wall per unit of floor area).

    • 6 × 6: 0.67 m exterior wall per m² floor

    • 7 × 7: 0.57 m exterior wall per m² floor

    A lower P/A ratio is better for reducing heat loss, so from that perspective the 7 × 7 wins marginally.

  • Total Heat Loss: Even though the 7 × 7 has more area to heat, its slightly more favorable P/A ratio means each square metre loses a bit less through walls, windows and roof.

  • Absolute Energy Demand: 49 m² of living space still needs more total heat (and cooling) than 36 m².


Which to pick?

  • If absolute energy use (and construction cost) is your top goal: go with 6 m × 6 m. You’ll heat/cool far less total volume.

  • If maximizing usable space while still keeping a tight envelope: 7 m × 7 m gives you ~36% more floor area, with only a ~5 % penalty in relative heat loss per m².


Quick rule of thumb

  • Small footprint & low volume ⇒ lowest bills.

  • But if you need room to live/feel spacious, the slightly larger 7 × 7 can be nearly as efficient per square metre and give more usable space.

Ultimately it’s a trade‑off between total energy/cost vs. usable area. If you’re OK with 36 m², the 6×6 is “best.” If you need closer to 50 m², the 7×7 is the sweet spot.

For a small, super‑insulated home in a temperate climate like Melbourne’s, you’ll want wall and floor assemblies that achieve U‑values on the order of 0.15 W/m²·K or better. In practical terms, that typically means:


External Walls

LayerThickness (mm)Notes
External cladding (timber, fiber‑cement, etc.)12–20Rain screen or weatherboard
Rigid continuous insulation (e.g. PIR, XPS)60–80λ ≈ 0.022 W/m·K; helps eliminate thermal bridging
Stud cavity insulated (e.g. Rockwool, glass wool)140–170For a 90–140 mm stud wall, full‑depth fill
Internal lining (plasterboard + air gap)12–15Allows vapour control layer
Total insulation depth200–250Typical overall wall thickness ~260–285 mm
  • Why 200–250 mm total?

    • A 90 mm timber stud cavity fully packed with dense‑packed wool gives around R3.0–3.5 m²·K/W.

    • Adding 60–80 mm of exterior PIR raises it to R8.0–9.0 m²·K/W (U ≈ 0.11–0.12 W/m²·K).

    • This assembly keeps thermal bridging and air leakage to a minimum while staying buildable with standard materials.


Ground Floor / Slab

LayerThickness (mm)Notes
Concrete slab (reinforced)100–150Acts as thermal mass
Under‑slab rigid insulation (XPS/PIR)75–100λ ≈ 0.028 W/m·K; continuous under slab
Edge insulation (perimeter)50–75Around slab edge to reduce thermal loss
Damp‑proof membrane0.2–0.3PE sheet below slab
Total insulation depth125–175Overall slab plus insulation ~225–325 mm
  • Why these depths?

    • 75–100 mm of under‑slab insulation yields R2.5–3.5 m²·K/W—enough to keep slab heat loss low.

    • Perimeter boards (50 mm) cut edge losses where heat can otherwise wick into the ground.


First‑Floor (Timber Joist)

If you have a suspended timber floor instead of slab:

LayerThickness (mm)Notes
Joist cavity insulation (batts)200–250Full‑depth mineral wool/Roxul
Under‑floor airtight barrier1–2 (foil)Reduces convective loops
Flooring (plywood + finish)20–25Standard floor build‑up
Total depth220–275Joist size ~200–240 mm
  • A 200 mm deep joist filled with dense mineral wool gives R6.0–7.0 m²·K/W (U ≈ 0.14 W/m²·K).


Summary of Recommended Thicknesses

  • Walls: 200–250 mm total framing + insulation.

  • Slab floor: ~125–175 mm insulation under a 100–150 mm slab (total ~225–325 mm).

  • Suspended floor: joist cavity 200–250 mm + finishes (~220–275 mm).

Those assemblies will comfortably hit U‑values of 0.10–0.15 W/m²·K, keeping your small house’s heating and cooling loads to an absolute minimum.

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To be continued 

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