Heat Recovery Ventilation for Energy-Efficient Buildings: Design, Operation and Maintenance

Abstract

Since the 1990s, many efforts have been intensified to fight global warming and energy crisis. Considering that the building sector is responsible for about 40% of the EU energy use and 36% of CO 2 emissions, many sustainable concepts have been revived from the past, a number of new innovative technologies have been invented, and new construction standards and policies have been implemented. Sustainable architecture offers tailor-made solutions to minimize the negative environmental impacts of buildings without compromising its users' comfort. According to studies, humans spend about 90% of their live-time indoors; indoor air quality has a major effect on human health. Hence, bringing fresh air into all habitable areas without letting the warm/cool air escape has become a priority. If properly operated and maintained, heat recovery ventilation (VHR) in energy-efficient buildings leads to an increased filtration and removal of micropollutants, and an overall improvement of the indoor air quality, thus generating more comfort and less health-related problems. A systematic case study in Italy is used in this research providing evidences of the effectiveness of mechanical ventilation heat recovery systems. This paper discusses a case with a combination of poor design, operation and maintenance to answer the questions of: what are the concerns about potential failures that are associated with these systems; and are there any cons in the technical aspects of a mechanical heat recovery ventilation system?

Full text

International Journal of Innovative Technology and Exploring Engineering (IJITEE)
ISSN: 2278-3075, Volume-9 Issue-1, November 2019
3713
Published By:
Blue Eyes Intelligence Engineering
& Sciences Publication
Retrieval Number: A4795119119/2019©BEIESP
DOI: 10.35940/ijitee.A4795.119119
Abstract: Since the 1990s, many efforts have been intensified to
fight global warming and energy crisis. Considering that the
building sector is responsible for about 40% of the EU energy use
and 36% of CO2 emissions, many sustainable concepts have been
revived from the past, a number of new innovative technologies
have been invented, and new construction standards and policies
have been implemented.
Sustainable architecture offers tailor-made solutions to
minimize the negative environmental impacts of buildings without
compromising its users' comfort. According to studies, humans
spend about 90% of their live-time indoors; indoor air quality has
a major effect on human health. Hence, bringing fresh air into all
habitable areas without letting the warm/cool air escape has
become a priority.
If properly operated and maintained, heat recovery ventilation
(VHR) in energy-efficient buildings leads to an increased
filtration and removal of micropollutants, and an overall
improvement of the indoor air quality, thus generating more
comfort and less health-related problems. A systematic case study
in Italy is used in this research providing evidences of
the effectiveness of mechanical ventilation heat recovery
systems. This paper discusses a case with a combination of poor
design, operation and maintenance to answer the questions of:
what are the concerns about potential failures that are associated
with these systems; and are there any cons in the technical aspects
of a mechanical heat recovery ventilation system?
Keywords: Passivhaus, Energy efficiency, HVAC, Indoor air
quality, Sustainable architecture.
I. INTRODUCTION: INDOOR AIR QUALITY AND
OCCUPANT’S HEALTH
According to the United States Environmental Protection
Agency (EPA), indoor environments can be much more
polluted than outdoors even in large metropolitan areas (EPA,
n.d.). Many people are at high health risks in their own homes
due to the extensive exposure of indoor pollutants. In
developed and temperate countries, it is estimated that
individuals spend 70% of their live-time in their private
homes, 20% in buildings, and 10% working outside or in
transport (as cited in BenGhida, 2016). It was estimated that
indoor pollutants are 1,000 times more likely to be inhaled by
occupants than comparable outdoor pollutants due to
improperly air ventilation and air renewal (California Air
Resources Board, 2005).
Revised Manuscript Received on November 05, 2019.
On the other hand, indoor air emissions have a direct
economic impact on cities and countries, e.g. California loses
more than $45 billion a year in direct medical expenses and
worker productivity and efficiency (Ibid).
Besides radon, which is the natural undetectable
radioactive gas that accumulates in enclosed spaces
(BenGhida, 2016), building materials and furnishings,
appliances, human activities, tobacco smokes, pets, devices
for combustion, chemical products, air conditioning and
ventilation systems are the main man-made sources of high
indoor levels of air pollutants. These indoor contaminants can
be found at very high rates in energy efficient buildings where
airtightness is very important (Arundel et al., 1986).
Humidifiers are usually used not only for minimization of
adverse health effects but also to increase indoor comfort
conditions and building durability. If not properly maintained
and sterilized these humidifiers will have a negative effect,
first, on the occupants due to microbial contamination, and
second, on the building structure due to fungal growth or mite
infestation (Arundel et al., 1986).
Figure 1. Optimum relative humidity range for minimizing
adverse health effects (Arundel et al., 1986)
Figure 1 shows the optimum relative humidity (RH) zone
for minimizing adverse health effects related to the indoor
relative humidity. Most biological and chemical aspects
increase in severity below 40% and/or above 60% (fig.1).
Mortality due to influenza and respiratory diseases might be
decreased in regions with low RH during winter seasons by
increasing it (Arundel et al., 1986).
Heat Recovery Ventilation for Energy-Efficient
Buildings: Design, Operation and Maintenance
Ben Ghida, D.

Heat Recovery Ventilation for Energy-Efficient Buildings: Design, Operation and Maintenance
3714
Published By:
Blue Eyes Intelligence Engineering
& Sciences Publication
Retrieval Number: A4795119119/2019©BEIESP
DOI: 10.35940/ijitee.A4795.119119
Figure 2. Formaldehyde concentration by ventilation system
type (Rudd and Bergey, 2013)
Figure 2 shows indoor formaldehyde concentration
measurements in the main and master zones in two different
houses during baseline test and four different ventilation
systems.
An Energy Recovery Ventilator (ERV) acts exactly as an
HRV while keeping some of the indoor air moisture. The
selection choice between an HRV or an ERV depends on four
factors: 1) the climate, 2) the number of house users, 3) the
specific personal needs (e.g. heath conditions), 4) and the
house size and volume. The ERV system gives an optimum
result for formaldehyde abatement, however, it is important to
mention that Rudd and Bergey did their experiment with
different air changes per hour for the five ventilation systems
(Rudd and Bergey, 2013).
II. HOW DOES A HEAT RECOVERY VENTILATOR
WORK?
HRV units (air-to-air heat exchanger) provide continuous
clean, fresh, and filtered air from the outdoor to the living
indoor and exhaust stale air from high moisture spaces:
kitchens, laundries, and bathrooms (fig.3).
Up to 95% of exhaust air heat can be recovered by
transferring it to the incoming air (depends of HRV model and
brand). Indoor comfort is ensured by smart sensors that
monitor the relative humidity and supplied air that adjust
automatically the indoor air quality with minimum heat loss.
Depending on installed windows quality, air permeability of
the architectural project and climate zone, HRV can save up
to 30% in heat energy (Manz et al., 2000; Juodis, 2006).
Figure 3. Heat energy ventilator
The HRV also known as the heat recovery air exchangers
are equipped with two continuously running fans. The first
one expels indoor stale air (saturated with smells, smoke,
pollutants, etc.), and the second one supplies fresh filtered
outside air. The fresh new air and expelled stale air never
come into contact with each other; the air is not
recycled. This technology captures heat or cooled energy and
recycles it; it does not generate it. It can recover heat during
winter or cool during summer from the expelled stale air, and
transfers it to the fresh incoming filtered air. The available
HRV with cross-flow in the Italian market has a varying yield
between 70-95% satisfying the actual EU ventilation standard
for single family dwellings EN 13141-7: 2010.
A frost protection control is activated when the outdoor
temperature is below the freezing point 0 °C to prevent the
freezing off the heat exchanger core; the HRV is put on a
standby mode. The antifreeze solution transfers the warm air
towards the core, and the damper closes off the cold
airstream. If the outdoor temperature rises again, the unit
returns to its normal working mode. The frost protection
control prevents the heat exchanger core from freezing
There are two types of HRV (fig.4):
 Centralized heat recovery ventilator (ducted): requires
an adequate ducting for air distribution installation. It
ventilates the whole house.
 Decentralized heat recovery ventilator (monobloc):
designed to be installed directly in the wall or in a glass
in contact with the outside. Ventilate the one single
space or room.
Figure 4. Centralized (Ducted) HRV vs Decentralized
(monobloc) HRV
Filters, as well as the exterior vents, should be removed and
cleaned four times per year on a regular basis.
III. BALANCING THE HEAT RECOVERY
VENTILATOR
HRVs are designed to maintain a quasi-neutral indoor
pressure by creating an equal balance between the incoming
and outgoing air. However, the balance might not be reached
in these cases:
 The HRVs are improperly regulated which creates a
negative indoor pressure similarly to an unregulated
exhaust fan, which on its turn can cause appliances
combustion and inefficiency of the ventilation system
 There is a stack effect
 The HRV is ducted to an existing HVAC ductwork
 Radon gas mitigation fan
 Existing exhaust fans (e.g. WC fans)
 Doors and windows opening
 Natural gas appliances that pull indoor air for
combustion
IV. ADVANTAGES AND DISADVANTAGES OF
MECHANICAL HEAT RECOVERY VENTILATOR
UNITS
Table 1 presents the most important pros and cons of an
HRV use and installation in residential buildings.

International Journal of Innovative Technology and Exploring Engineering (IJITEE)
ISSN: 2278-3075, Volume-9 Issue-1, November 2019
3715
Published By:
Blue Eyes Intelligence Engineering
& Sciences Publication
Retrieval Number: A4795119119/2019©BEIESP
DOI: 10.35940/ijitee.A4795.119119
Table 1. Pros and cons of heat recovery ventilator units
Advantages
Disadvantages
Maximum energy efficiency
thanks to heat recovery systems:
Up to 95% recovery (depends on
HRV model installed)
Works efficiently in
well-insulated and airtight
buildings
Compact in size of the main
control unit
Larger encumbrance of the
insulated air supply/exhaust
pipes, and air distribution ducts
Rapid initial investment
amortization (in extreme
climates)
Important initial investment
Can be used for heating and
cooling
Filters need to be cleaned every
3 months (or replaced)
Reduction or elimination of
chiller, piping, technical center,
chimney, etc.
-
Static or dynamic management of
overpressure or depression in
every individual space.
-
Reduction of connected load and
consumption (kW) for heating
and cooling
-
Continuous clean, fresh, filtered
air supply: elimination of
irritants, allergens and air
pollutants
-
Moisture control: mold formation
prevention
-
Maintain comfortable constant
temperature
-
Children and elderly well-being
-
Indoor acoustical comfort (silent)
-
Smart management: sensors
constantly monitor the relative
humidity and adjust the supplied
air volume/air flow
-
Reduce greenhouse gas emissions
-
V. COST-EFFECTIVENESS OF AN HRV
To simplify the comparison, I will use an average
electricity price for Italian household consumers (taxes
included) of 0.2067 €/kwh which was determined for the first
half 2018, as provided by Statistics Explained from the
European Union portal (Eurostat, 2018). Obviously, the
Italian market is much more open and competitive and offers
many solutions and opportunities to spend less. An annual
energy consumption comparison of different household
appliances with a standard HRV is shown in Table 2. The
selection of the heat recovery ventilator system depends on
the number of house occupants, climate, and the volume size
of the house to be ventilated. Thus, the energy consumption of
an HRV varies from 50Watt to 100Watt and even more for
bigger houses. The costs vary from €10,300 to €12,100 for an
HRV unit and its full installation inside a 100m2 house. The
Law no. 190 of December 23, 20141 encourages the use of
new technologies towards energy conservation and energy
efficiency in buildings; it is possible for home owners to get a
50% tax deduction and in some circumstances, it can reach up
to 65%.
It is important to mention that the recovered thermic watts are
much higher than the consumed electrical watts, and of course
it is much cheaper to heat dry air than humid air.
1Known as the 2015 Stability Law, for documented expenses related to the interventions
referred to in Article 16-bis, paragraph 1 of the Decree of the President of the Republic
December 22, 1986, n. 917
Table 2. Comparison of annual energy consumption of the HRV
unit vs household appliances
Designation
Watt
Estimated use
Yearly
consumption
[kwh]
Annual
cost [€]
20-Watt LED
Bulb
20
4 hours/day
29.2
6.03
Hairdryer [With
only 1 speed]
2800
2 hours/month
67.2
13.89
Fan [with 4 #
speed]
180
8 hours [speed
2]/6months
64,4
13.31
Combi
fridge-freezer
200
Continuously
201
41.55
LED TV
60
4hours/days
54
11.16
HRV
50~100
Continuously
[~75Watt]
~657
135.80
VI. CONCLUSIONS
Providing clean and fresh indoor air into our homes is
essential for a healthy livable environment. Controlled
mechanical heat recovery ventilation do not only provide
clean and fresh air but it also contributes to the building’s
energy efficiency and global warming mitigation. With the
“2015 Stability Law”, the Italian government is working to
build a healthier and more sustainable country, encouraging
the population to use the latest buildings cutting-edge
sustainable technologies. Disadvantages outlined in this paper
are almost negligible in comparison with the huge benefits
that the HRVs are bringing to homeowners. The initial
investment cost of an HRV are worthy for a healthy family.
However, this is not a ready-to-use high-tech technology;
because the study, installation and calibration of HRVs must
be done by professionals. Any oversizing, negligence, or
misuse can compromise the efficiency of the system and
affect negatively the house user’s health.
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