Building's indoor climate can be evaluated based on the following criteria:

• A correct thermal-humidity microclimate is the most important element for ensuring a healthy indoor environment of buildings.
• The recommended hygienic value of higher air RH (50 to 70 %) that prevents dryness of mucous membranes, commonly causes mold formation (e.g. the Alternaria or Aspergillus family), mainly in cool and poorly ventilated room corners, heads and linings. This results in increasing resident sickness figures, frequent nausea, alergies, bronchitis etc.
• Those phenomena gain strength when inappropriately weatherstripping windows without an appropriate air intake compensation. In addition, with higher RH value (above 60 %) percentage of surviving organisms doubles (e.g. Staphylococus, Streptococus) in respect to RH value of 30 to 40 %. With decrease of the RH value number of mites in textiles and resulting alergies (asthma) dramatically decreases.
• To the major humidity sources in buildings belong mainly human methabolism (produces 50 to 250 g of water vapor/h/1, based on activity), bathrooms (produce 700 to 2600 g of water vapor/h), kitchens (produce 600 to 1500 g of water vapor/h) and laundry drying (produce 200 to 500 g of water vapor/h/5 kg).
• In many rich counties it is recommended for keeping the optimum RH value (between 35 to 45 %) that a forced ventilation of apartments with ACH value of n = 0,3 to 0,5 h^-1 be applied.
• Microbical microclimate is created by microorganisms of bacteria, viruses, fungi, spores and pollens. Alergic syndroms from spores of different types of fungi and pollen particles become very serious problem these days. The most efficient method to reduce the mircobical concentrations in buildings till now is a thorough ventilation using clean outdoor air.
• Aerosol microclimate - aerosols occure in air in form of solid particles (dust) or fluid particles (mist).
• Building dust, mainly particles smaller than 1 mikrometer, is other main cause of asthma.
• Odour microclimate - next to a common odours (smoke, food preparation) styrenes, formaldehydes and paint vapors, substances not known before, occure in today’s interior.
• In general, concentration of 0,10 % CO₂ (Pettenkofer kriterion) is stated as a comparative and exact measured value; for removal of feeling of stale air caused by human odours even 0,07 % CO₂ (700 ppm = 1 300 mg/m³) value is used.
• Quality of odour microclimate in buildings can only be affected basically a sufficient intake of fresh air. Basic and worldwide recognized value of ventialtion intensity for removal of common body odours (for not addapted persons) is 25 m³/hod of fresh outdoor air per person.
• Toxic microclima is created by toxic gasses with pathological effects. The most unhealthy gas in buildings’ interior is CO. Poorly ventilated kitchens with gas stoves have NO_x occurence up to 50 micrograms/m³ which has evidently cancerogenic effect.
• Higher concentration of formaldehyde causes irritation of eyes and mucous membranes. It also is an allergen and potential cancerogen.

Present state

Tougher requirements on quality of residential building envelope and reduction of uncontrollable infiltration through cracks bring many problems:

• natural interior airchange declines below n < 0,05 h^-1 which is totally unacceptable from a hygienic point of view
• with stable average-family water vapor production in an apartment (up to 10 l/day) fungi with very negative effects to human health occure
• condensed moisture has a negative effect on appearance and lifetime of building structure
• reduction of building heat loss brings problems with balancing of standard water heating systems
• buildings overheat due to a summer solar gain almost without possibility of natural ventilation

Rules for low-energy buildings

The new issue of CSN 730540 - 2 (2002) Thermal insulation of buildings adopted in accordance with the EU much tougher values of heat transfer factors through all exterior structures. Also, new hygienic requirements are specified for air change in buildings, use of controlled ventilation with heat recovery, as well as building leakage (air-tightness) control in accordance with CSN EN 13829 (blower - door test).

Purpose of these radical changes is above all reduction of building operation energy use and improvement of the indoor air quality.

The future belongs to low-energy residental building with calculated heat consumption for heating is lower than 50 kWh/m²/year, with the following major rules defined:

1. Suitable building orientation
2. Orientation of rooms south for utilization of pasive solar gains
3. Compact building shape (A : H ratio) with optimum glazing area
4. Avoidance of thermal bridges
5. Very low heat transfer values for the building envelope: exterior walls: U < 0,15 W/m²K; roof: U < 0,12 W/m²K; windows: U < 1,1 W/m²K
6. Low energy cost of building materials production (suitability of wood buildings)
7. Perfect tightness of the whole building (measured by the Blower door test according to EN 13829, i.e. n < 0,9 h^-1 at Δp = 50 Pa)
8. Installation of controlled ventilation with heat recovery, preferable in combination with a flexible warm-air heating and indoor heat gain utilization
9. Installation of bivalent (supplemental) biomass heat source (fireplace insert, stove)
10. Installation of solar systems to support space and HSW heating, with low-temperature accumulation
11. Use of low-energy appliances

Comparison of energy parameters

Parametr	Unit	Old method of building family houses	Low-energy houses NERD)	Energy pasive houses EPD)
Heating & ventilation heat consumption 1)	kWh/rok	up to 25 000	up to 9 800	< 2 100
Specific calculated heat input for heating & ventilation	W/m2	> 110	20 - 40	< 10
Specific heat consumption - for space heating and forced ventilation	kWh/m2a	170 - 220	30 - 70	d 15
Specific heat consumption - for HSW heating	kWh/m2a	35	< 20	10 - 15
Specific consumption of electric energy in household (EL)	kWh/m2a	30	< 20	10 - 15
Total specific consumption (SH + AHU + HSW + EL)	kWh/m2a	235 - 285	70 - 110	35 - 45
Total specific consumption of primary fuel PEZ	kWh/m2a	-	-	< 120
Min. required heat transfer factor - through walls	W/m2K	-	< 0,20	< 0,12
Min. required heat transfer factor - through windows	W/m2K	-	< 1,00	< 0,85
1) average family house of 140 m2 of utilized area internal gains in EPD houses cover up to 35% of total heating heat consumption; solar gains up to 30 %, with remaining consumption approx. 35 % central Europe climate prefers internal gains to solar gains, with window area not exceeding 30 % of facade area

Recommended microclimate values for residences

Parametr	Symbols & units	Heating season		Summer
		optimum	acceptable	optimum	acceptable
Indoor temperature	ti [°C]	20,8 +/- 0,8	18 - 24	26 +/- 0,5	22 - 28
Relative humidity	rhi [%]	30 - 55	20 - 70	-	-
Air movement	w [m/s]	max. 0,15	max. 0,20	max. 0,15	up to 1,0

Requirements for room ventilation

Regulation	Air change rate [h-1]	Ventilation air volume
DIN 4701	0,5	-
VDI 2088	0,4 - 0,8	-
NKB Publication	≥ 0,5	30 m3/h
ECE Compendium	≥ 0,5	-
BSF 199838	0,4	1,26 m3/h m2
ČR ČSN 06 0210	0,5	-
ASHRAE USA	-	27 m3/h person
SIN 06 0210	≥ 0,5	-

Requirements for kitchen, bathroom and WC ventilation

Regulation	Kitchen		Bathroom		Separate WC
	[m3/h]	[h-1]	[m3/h]	[h-1]	[m3/h]	[h-1]
DIN 18017/3	-	-	40 - 60	-	20 - 30	-
DIN 1946/6	40 - 60	-	40 - 60	-	20 - 30	-
ECE Compendium	36 - 180	-	36 - 180	-	-	-
BSF 199838	36 - 54	-	36 - 108	-	36	-
ČR	100 - 150	≥ 3	60	3 - 5	25	3

Water vapour production values

Water vapour sources	Vapour production [g/h]		Water vapour sources	Vapour production [g/h]
bathtub	700		houseplants	5 - 20
shower	2 600		Gas stove operation - gas combustion	1 500 g / 1 m3 of gas
cooking - hot meals	600 - 1 500		Floor wiping, wet cleaning	1 000
cooking - daily average	100		Resting person	30
Laundry drying - spinned	50 - 200		Light work	40 - 200
Laundry drying - wet, dripping	100 - 500		Moderate work	120 - 200
Washing machine	300		Hard work	200 - 300
ironing	200

Comparing parameters of residental heating and ventilating systems

Ensuring of required parameters	Standard hot-water heating				Warm-air circulation heating
	with window infiltration	weatherstriped windows (occasional ventilation)	with bathroom exhaust	with controlled ventilation & heat recovery	with controlled ventilation & heat recovery	with controlled ventilation heat recovery & ground exchanger
Thermal comfort	accomplishes completely	does not accomplish	accomplishes partially	accomplishes completely	accomplishes completely	accomplishes completely
Room ventilation	accomplishes completely	accomplishes partially	accomplishes partially	accomplishes completely	accomplishes completely	accomplishes completely
Occasional ventilation ("party" mode)	does not accomplish	does not accomplish	does not accomplish	accomplishes completely	accomplishes completely	accomplishes completely
Bathroom exhaust	does not accomplish	does not accomplish	accomplishes partially	accomplishes completely	accomplishes completely	accomplishes completely
Air change efficiency	accomplishes partially	does not accomplish	does not accomplish	accomplishes partially	accomplishes completely	accomplishes completely
Heat recovery	does not accomplish	does not accomplish	does not accomplish	accomplishes completely	accomplishes completely	accomplishes completely
Internal & external gain usage	does not accomplish	does not accomplish	does not accomplish	accomplishes partially	accomplishes completely	accomplishes completely
Supply air filtration	does not accomplish	does not accomplish	does not accomplish	accomplishes completely	accomplishes completely	accomplishes completely
Night precooling	does not accomplish	does not accomplish	does not accomplish	accomplishes partially	accomplishes completely	accomplishes completely
DX cooling	does not accomplish	does not accomplish	does not accomplish	does not accomplish	accomplishes partially	accomplishes completely

Problems caused by poor ventilation of residental rooms

Building damage by moisture	Mites	Fungi Alergies	Molds Alergies	Resident sickness