One of the features in our new house that I’m most excited about barely raises an eyebrow with some of our visitors: the ventilation system. I believe we have the highest-efficiency heat-recovery ventilator (HRV) on the market — or at least it’s right up there near the top.I’ll describe this Zehnder HRV and its impressive specifications and features — but not until next week. This week I’ll provide a little background on ventilation. Ventilation optionsVentilation can take many different forms. Very generally, systems can be categorized into about a half-dozen generic types:No ventilation. This is almost certainly the most common option in American homes. There is no mechanical system to remove stale indoor air (and moisture) or bring in fresh outside air. In the distant past, when buildings weren’t insulated, this strategy worked reasonably well — relying on the natural leakiness of the house.It’s worth noting, though, that even a leaky house doesn’t ensure good ventilation. For this strategy to work there has to be either a breeze outside or a significant difference in temperature between outdoor and indoors. Either of these conditions creates a pressure difference between indoors and out, driving that ventilation. On calm days in the spring and summer, there might be very little air exchange even in a really leaky house.Natural ventilation. In this rather uncommon strategy, specific design features are incorporated to bring in fresh air and get rid of stale air. One approach is to create a solar chimney in which air is heated by the sun, becomes more buoyant, and rises up and out through vents near the top of the building; this lowers the pressure in the house, which draws fresh air in through specially placed inlet ports. The rest of this blog will focus on mechanical ventilation.Exhaust-only mechanical ventilation. This is a relatively common strategy in which small exhaust fans, usually in bathrooms, operate either continuously or intermittently to exhaust stale air and moisture generated in those rooms. This strategy creates a modest negative pressure in the house, and that pulls in fresh air either through cracks and other air-leakage sites or through strategically placed intentional make-up air inlets. An advantage of this strategy is simplicity and low cost. A disadvantage is that the negative pressure can pull in radon and other soil gases that we don’t want in houses.Supply-only ventilation. As the name implies, a fan brings in fresh air, and stale air escapes through cracks and air-leakage sites in the house. The air supply may be delivered to one location, dispersed through ducts, or supplied to the ducted distribution system of a forced-air heating system for dispersal. A supply-only ventilation system pressurizes a house, which can be a good thing in keeping radon and other contaminants from entering the house, but it risks forcing moisture-laden air into wall and ceiling cavities where condensation and moisture problems can occur.Balanced ventilation. Much better ventilation is provided through a balanced system in which separate fans drive both inlet and exhaust airflow. This allows us to control where the fresh air comes from, where that fresh air is delivered, and from where exhaust air is drawn. Balanced ventilation systems can be either point-source or ducted. With ducted systems, it makes sense to deliver fresh air to spaces that are most lived in (living room, bedrooms, etc.) and exhaust indoor air from places where moisture or pollutants are generated (bathrooms, kitchen, hobby room).Balanced ventilation with heat recovery. If there are separate fans to introduce fresh air and exhaust indoor air, it makes a lot of sense to locate these fans together and include an air-to-air heat exchanger so that the outgoing house air will precondition the incoming outdoor air. This air-to-air heat exchanger — more commonly referred to today as a heat-recovery ventilator or HRV — is the way to go in colder climates. A slightly different version, known as an energy-recovery ventilator (ERV), is similar but transfers moisture as well as heat from one airstream to the other, keeping more of the desirable humidity in the house in the winter and reducing the amount of humidity introduced from outdoors in the summer. Alex is founder of BuildingGreen, Inc. and executive editor of Environmental Building News. In 2012 he founded the Resilient Design Institute. To keep up with Alex’s latest articles and musings, you can sign up for his Twitter feed. RELATED ARTICLES Designing a Good Ventilation System GBA Encyclopedia: Ventilation ChoicesAre HRVs Cost-Effective?HRV or ERV?A New Way to Duct HRVsVentilation Rates and Human HealthHow Much Fresh Air Does Your Home Need? Joseph Lstiburek: Just Right and Airtight Tight homes need mechanical ventilationI’ll focus more on HRVs in next week’s blog, especially our new high-efficiency Zehnder system. Following that I’ll address why commissioning an HRV is so important and how that’s done — or at least how it was done with our system.I’m a firm believer that all homes should have mechanical ventilation. With better-insulated, tighter homes, that ventilation is all the more important. But even in a very leaky house, one can’t count on bringing in much fresh air or calm days in the spring and fall when there isn’t a pressure differential across the building envelope.If budgets allow, going with balanced ventilation is strongly recommended, and if you’re doing that in a relatively cold climate, like ours, then providing heat recovery is a no-brainer. Mechanical ventilation always takes energy; with heat recovery the energy penalty of fresh air is minimized. Why ventilate?For centuries homes weren’t ventilated, and they did all right, didn’t they? Why do we need to go to all this effort (and often considerable expense) to ventilate houses today?There are several reasons that ventilation is more important today than it was long ago. Most importantly, houses 100 years ago were really leaky. Usually they didn’t have insulation in the walls, so fresh air could pretty easily enter through all the gaps, cracks, and holes in the building envelope.Also, the building materials used 100 years ago were mostly natural products that didn’t result in significant offgassing of volatile organic compounds (VOCs), formaldehyde, flame retardants, and other chemicals that are so prevalent in today’s building materials, furnishings, and belongings.
Lawyers from the Indian Association of People’s Lawyers have expressed their concern over the arrest of advocate Surendra Gadling from his house in Nagpur, alleging an attack on lawyers who are fighting cases of marginalised people.Mr. Gadling has been arrested in relation with the violence at Bhima Koregaon near Pune when Dalits congregated to celebrate the British victory over Peshwas with the help of Mahar soldiers.Addressing the media here on Thursday, IAPL vice-president Sudha Bharadwaj said that the sudden arrest was part of a pattern where “people’s lawyers” are being targeted, in violation of the widely-held norm that “being a lawyer of a political prisoner is not a crime”.A release by the IAPL said that this is part of a larger pattern: advocates Upendra Nayak of Odisha, Murugan of Tamil Nadu and Satyendra Chaubey of Chhattisgarh “have all been implicated in the cases of their own clients, which is absolutely unacceptable as per United Nations principles on the role of lawyers”.“In the morning of June 6, 2018, the Pune Police arrested senior advocate Surendra Gadling from his house in Nagpur at 6 a.m. The arrest has been made in connection with an FIR registered on January 8, 2018 at Vishrambaug PS in Pune. The FIR originally alleged inciting communal harmony at the Elgar Parishad program organised on December 31, 2018 to commemorate 200 years of the victory of Mahar soldiers over the Peshwa in the Bhima Koregaon battle,” the release said. “In March 2018, the case was converted into a criminal conspiracy. On April 17, 2018, though the FIR did not originally name advocate Gadling, the police raided his house and office and confiscated all possible CDs, hard disks, computer systems – including the family’s devices. Yesterday he and other intellectuals and activists were arrested in the same case, by adding several sections of the draconian Unlawful Activities Prevention Act (UAPA), which ensures long detention and difficulty in obtaining bail.”Apart from Mr. Gadling, head of the English department at Nagpur University Shoma Sen, Marathi poet Sudhir Dhavale, Rona Wilson of the Committee for the Release of Political Prisoners and anti-displacement activist Mahesh Raut have also been arrested.“The bias of the state is all the more obvious when the leaders of Hindutva organisations named in many complaints and FIRs as instigators of the Bhima Koregaon violence – Milind Ekbote and Sambhaji Bhide – whose anticipatory bail applications have been refused by even the Supreme Court, still roam free,” the release said.