Transferring the German Passivhaus fabric-first standard (superinsulation, high airtightness, mechanical ventilation) to hot-humid tropical dwellings has so far been evaluated only by simulation. Sigalingging, Chow and Sharples (2020) modelled a Jakarta terraced house upgraded to the Passivhaus standard and predicted that leaving the ground floor uninsulated — so the soil acts as a thermal sink providing radiant cooling — beneficially lowers indoor air temperatures; but this inference was never tested by measurement, the ground heat transfer model behind it is sensitive to poorly constrained soil assumptions, and the capital, life-cycle cost and supply-chain feasibility of such construction in Indonesia is unknown. The open questions are whether the ground beneath an airtight, superinsulated tropical dwelling really absorbs heat across a full cooling season, whether a ground boundary treatment for tropical cooling conditions can be made robust, and whether tropical Passivhaus construction is economically and practically feasible in Indonesia. No experimental, ground-model, or Indonesian cost study is known to resolve any of these threads.

Background

The Passivhaus (Passive House) standard is a fabric-first building energy standard, developed in Germany for cold climates, that combines a superinsulated and highly airtight building envelope with mechanical ventilation and a stringent energy budget administered through the Passive House Planning Package (PHPP), a design-verification calculation tool. Airtightness — making the envelope leak-proof so that uncontrolled air infiltration is minimized, typically verified by a fan pressurization ('blower door') test — and insulation cut both heating losses and, in principle, the conductive and infiltrative heat gains that drive cooling demand.

In a hot and humid tropical climate such as Jakarta's, the cooling problem is twofold: high air temperatures and high indoor relative humidity, usually ameliorated by energy-intensive air conditioning. Natural ventilation, the traditional tropical strategy, imports moisture, and a large fraction of cooling energy is lost through air infiltration. Applying the temperate-origin Passivhaus approach to tropical housing is therefore attractive but unproven: sealing and insulating the envelope could equally trap heat and moisture and increase mechanical cooling and dehumidification loads.

Sigalingging, Chow and Sharples (2020) took an actual terraced house in Jakarta and incrementally upgraded its insulation and airtightness in a dynamic thermal simulation using IES VE (Integrated Environmental Solutions' Virtual Environment, a commercial building thermal-modelling suite) up to the Passivhaus standard, validating the model of the existing house against short field measurements of indoor air temperature and relative humidity. A novel design variant emerged from the simulation: the ground-floor insulation was removed so that the ground floor slab couples directly to the soil and the soil acts as a thermal sink — a passive heat absorber that can cool the interior by drawing heat out of the building and radiating 'coolth' from the slab surface (radiant cooling). The simulation predicted a beneficial effect of this uninsulated floor on indoor air temperatures. However, the authors themselves flagged what remains unresolved. First, the floor-sink benefit is a simulation inference only; no field measurements of heat flux into the soil or floor surface temperature exist for such a dwelling, so it is unknown whether the soil will keep absorbing heat throughout an entire cooling season rather than saturating. Second, the modelling of floor heat transfer is complicated by soil conductivity, thermal storage, time delay, and seasonal weather change; the authors' companion study (Sigalingging, Chow and Sharples 2019) showed that the predicted air temperatures depended strongly on which ground-temperature model was assumed, with agreement to measured data in the base-case house achieved only under one particular model — evidence that ground boundary conditions are load-bearing and inadequately constrained for tropical cooling conditions. Third, insulation, double glazing, and airtight construction are not yet common practice in Indonesia, so capital cost, life-cycle cost, technical skills, construction quality, and supply-chain readiness for tropical Passivhaus housing are unassessed. Ground-coupled heat transfer — heat exchange between a building floor and the soil beneath, governed by soil thermal properties, moisture, and depth — is a classical building-physics topic, but its experimental literature addresses heat losses from heated buildings in temperate climates, not sustained heat rejection from superinsulated airtight dwellings in the humid tropics.

Problem Statement

For a hot and humid tropical climate (as represented by Jakarta, Indonesia), determine whether a dwelling upgraded to the Passivhaus envelope standard (superinsulation, high airtightness, controlled ventilation) with an uninsulated ground floor has a ground floor that reliably acts as a heat sink throughout an entire cooling season, absorbing heat from the building and providing sustained radiant cooling — cooling of the interior by long-wave exchange with the cooler slab surface — instead of saturating, i.e. warming up until the soil can absorb little further heat. The open sub-questions are (i) whether the floor heat flux, floor surface and indoor temperatures, humidity, and cooling energy in such a dwelling, together with the soil temperature profile beneath it, sustain heat absorption by the ground across at least a full cooling season; (ii) whether a ground-coupled floor heat transfer treatment for tropical conditions can be made robust to soil conductivity, thermal storage, time delay, and seasonal weather variation, replacing the ground-model sensitivity identified in the simulation literature; and (iii) whether this construction is economically and practically feasible in Indonesia — capital cost, life-cycle cost, and the technical skills, construction quality, and supply-chain readiness for insulation, double glazing, and airtight construction. These three components jointly serve one objective: establishing whether the Passivhaus standard, with ground-floor soil coupling as a passive cooling mechanism, is physically and practically viable for tropical housing.

References

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