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» Division: Residential ventilation warm-air heating

Ventilation and heating of residential pools

Present - day problems

Deterioration of perimeter walls of unventilated swimming pools due to excessive humidity

with insufficient evaporated moisture removal fromwater surface the RH value increases to a point, where a surface condensation of water vapor on building structure (thermal bridges) and whole surface of glazing takes place
the condensate seriously damages building structure, runs down the glazing and is unacceptable for a user
this is accompanied by occurrence of fungi (e.g. Cladosporium, Penicillium, Aspergillus versicolor)
in many cases there are no vapour barriers in walls, moisture enters the exterior walls, condenses and dramatically reduces their thermal insulating characteristic
in many cases there only are condensing dehumidifiers with insufficient airflow reach installed, does not cover the whole pool space, which results in heavy condensation and fungi occurrence in poorly ventilated space. At the same time, serious problems arise fromevaporated chemical disinfection (chlorine, ozone, and halogens - bromine, iodine, chloroform) fromthe water

Microclimatic parameters of pools

Typical fungi occurence in unventilated pool corners

air temperature	t_a = 30 °C
water temperature	t_w = 28 °C
air relative humidity	rh_i = 60 to 65 °C
air specific humidity	x_i = 17,0 g/kg

The following values are used for calculation and design of air-handling systems:

calculated difference of specific humidities of indoor and outdoor air – for winter	Ø Δx_ie = 14 g/kg
calculated difference of specific humidities - for off season	Ø Δx_ie = 10 g/kg
calculated difference of specific humidities - for summer	Ø Δx_ie = 5 g/kg

The following empiric values are used for determining the amount of evaporated water fromthe pool surface
(for common temperatures t_a / t_w = 30 / 28 °C)

Residental pools in operation	ΣX = 180 g/m² h
Still water surface	ΣX = 55 g/m² h
Covered water surface	ΣX = 8 g/m² h

These values are put in the following equation to calculate required ventilation rate:

where:

F_B	Water surface area [m²]
ρ	Supply air density [kg/m³]

For common cases approximate specific ventilation requirements can be determined (i.e. Fresh air intake and stale air exhaust) based on season:

winter season	V₁ = 11 m³/h m²
off season	V₁ = 16 m³/h m²
summer season	V₁ = 32 m³/h m²

Rules for economical solution of residential pool design

choose a building envelope with the best thermal insulation and technical parameters
avoid unnecessary large glazing (mainly in pool roofs)
totally eliminate thermal bridges
design perfect vapor barriers for walls and roofs
design rectangular pool shapes to easily install rolling foil covers, possibly insulating cassettes made of polyurethane
design connections to house only through a tight door, preferably through separately ventilated corridor
in respect to possible losses and condensation in ducts locate the ventilating unit as close as possible to pool

Rules for ventilation and heating of residential pools

The rules come fromexperience with many newly built or retrofitted pools in Czech Republic in recent years:

ensure thorough ventilation of the whole space; avoid poorly ventilated corners with possible condensation
always ensure supply of dry warmair with low RH value on glazing with sufficient speed and reach
keep the whole space in negative pressure (min. 95 %) to avoid risk of water vapor escaping into adjacent spaces or into a structure through an incorrectly made vapor barrier
always design the ceiling distribution ductwork in the pool made of stainless material with slot or nozzle outlets; possibly of aluminumfinished polyurethane, with slot outlets without control (due to complicated access)
ensure perfect tightness of stainless floor ductwork, sloping towards a condensate drain, access for cleaning and excelent thermal insulation
design air distribution ductwork outside the pool of tight duct (e.g. Polyurethan), sloping towards a condensate drain, and thermaly insulated. Never install exhaust grilles in false ceiling through a cut vapor barrier!
design suction grille centrally opposite the glazing, under the space ceiling
design the air distribution for very small spaces (e.g. with only one window or in a basement) only by a central jet air outlet (adjustable)
always isolate the pool air-handling systemfromthe one serving the house, including supply and exhaust ducts, to avoid drafts (backdraft dampers do not guarrantee continuous and trouble-free opeartion)
due to unsteady residential pool opeartion (e.g. 1 – 2 hours a day) it is ideal to install the air-handling systemwith warm-air heating to achieve required air temperature quickly, in just several dozens of minutes (with thermal insulation and vapor barrier on the wall inside).
air-handling units for pools must be suitable for aggresive environmet (chlorine), i.e. With heat recovery core made of stainless or plastic material, condensate drain pan of stainless steel or with a special finish
it is recommended that as a basic heating system a floor distribution system be installed with connection to a low-temperature heat source (HP, solar energy), possibly a system of floor-standing convectors under windows, with excelent anticorrosive finish with a special design to avoid human injury

DUPLEX RDH UNITS

Units of the DUPLEX RDH series are designed for dual-zone warm-air circulation heating with simultaneous ventilation with heat recovery for swimming pools.
Unlike the units for residential applications, the RDH units are made of stainless steel sheets, increasing their corrosion resistance for using in swimming pools.
For more information see the unit ventilator.

Ventilating and heating modes of a duplex rdh pool unit

Circulation heating and ventilating mode (mode 2)
	Warm-air circulation heating and equal-pressure ventilation with heat recovery controlled automatically by a humidistat and a thermostat; with circulating and ventilation air volume up to 1 800 m³/h and 500 m³/h respectively. Both fans ON, mixing damper in position "1".
Circulation heating mode (mode 3)
	Used for heating and tempering of pools during off hours. Exhaust fan OFF, mixing damper in position "0". When RH increases, mode 2 is set automatically. Temperature is controlled by a room thermostat.
Positive-pressure ventilating mode (mode 5)
	Intensive summer positive-pressure ventilation at full outdoor air intake (possibly via a ground exchanger). Air exhaust through open windows. Mixing damper in position "2", by-passu damper open.

c₁	Inlet of circulating air into the unit
c₂	Outlet of circulating air from the unit
e₁	Inlet of fresh outdoor air into the unit
e₂	Outlet of fresh air from the unit
i₁	Inlet of exhaust (stale) air into the unit
i₂	Outlet of exhaust air from the unit

Note:

Operating modes 1 and 4 are not used for pools.
Ductless distribution with nozzle air outlets can only be used for the smallest pools without glazing (L_max = 5 m)

Cross section of pool ventilation


Longitudal ventilation air supply above windows or glazing; distribution ductwork of polyurethan with aluminum finish. Air distribution through nozzles above glazing, centralized air exhaust through a stainless grille.	Longitudal ventilation air supply in glazing; distribution round ductwork of AISI 304 stainless sheets. Air distribution through perforation or nozzles vertically or under an angle on glazing.