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Comment by maxsilver | Hacker News Reader

From the article's description, apparently "Passive House" means "no cooling whatsoever", which explains why it's not common in the US.

Don't get me wrong, we need stronger building standards and better insulation. Especially in the US, where we let literally any hollow twig+glue structure stand with essentially no quality checks whatsoever.

But the reason everyone "throws a solar panel on top to get Net Zero", is because it gives you cheap green electricity to run both heat and Air Conditioning. There are precious few places you could build this thing in the US where it won't be annoyingly hot to live in for at least 3+ months every year. Even in Michigan, a building is essentially broken if it doesn't have AC, if not for the heat then to at least remove the moisture / humidity / condensation built up.

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You don't need AC to remove humidity. MVHR removes it and dumps it into the drains when the warm outgoing air goes through the air to air heat exchanger to warm up the incoming air.

Then where does the heat from your dehumidifier go?

MVHR seems to assume outside air is always cooler and fresher than inside air, and uses that for free cooling. Which is great for like 70% of the time. But what about the ~30% of time when it isn't there.

It doesn't assume that. MVHR has a bypass to disable the heat exchanger if that's important.

You don't have a dehumidifier. One of the biggest benefits of fabric first is the reduction in complexity.

If you don't have a dehumidifier, all of those big bags of mostly water that inhabit the building will expel some of that water with every breath, and going to increase the humidity fairly noticeably.

I'm also going to guess that the MVHR is also not 100% efficient. It's either going to create heat to completely cool down the incoming air (hey, look, an AC, complete with dehumidification), or the incoming air is going to average out with the out going air, creating an increase in temperature.

Plus, all of those bags of mostly water are going to be expelling heat, too.

MVHR dehumidifies the air inside, I explained in another comment above. We have used units which are 96% efficient.

MVHR is a ventilation system - it removes the humidity.

A decent MVHR runs at double figures in terms of watts, so like an old fashioned light bulb.

what are you talking about? who mentioned a dehumidifier? mvhr simply exchanges air without changing its temperature. its not great for cooling or heating by its very definition. its good for humidity and freshness. using insulation and hr ventilation simply allows you to have a heating and air conditioning solution that is massively reduced in size. in some cases none at all.

Warming incoming air is the opposite of what people in the US mean by "air conditioning". It seems to me that what you are describing is the opposite of how thermodynamics works. Warm air holds more moisture and condensation occurs when air is cooled below the dew point.

I was responding to the point about using AC all year to remove humidity. The thermodynamics works like this: The air inside your house is more humid than the air outside; warm air at the same pressure holds more moisture than cold air. When you extract the warm air from the house the heat exchanger cools it down, therefore reducing its moisture carrying capacity and causing condensate to form which you can remove. The heat is transferred to the incoming cold air via the heat exchanger, the warmed up incoming air now has a much greater water carrying capacity even if it was already humid outside so it absorbs humidity from your house, when this air is extracted again the cycle repeats. Passive houses have very low humidity inside because of this.

> I was responding to the point about using AC all year to remove humidity.

That's not something I claimed.

Most people in the US are only using AC in the summer (or warm season), to remove humidity from their home when the humidity outside is much higher than indoors.

Sorry I was confused when you said “if not for the heat then to at least remove the moisture”. When your insulation is being used to keep heat out, your heat exchanger would operate in reverse to use extract air to cool incoming air, some MVHR units have optional precooling of incoming air. I expect a modern standard AC unit will be doing some cold recovery as well to improve efficiency. But ideally a fabric first approach will keep a lot of heat out when combined with external blinds and brise soliel to keep high angle summer sun out.

The "even in Michigan" was carrying implicit information. The relative humidity outside right now it 51%. It's -10°C, the dew point is -18°C.

So during the winter houses that aren't incredibly well sealed need humidification more than they need dehumidification.

During the summer it gets quite humid even when the temperature isn't all that high.

> From the article's description, apparently "Passive House" means "no cooling whatsoever", which explains why it's not common in the US.

That's not what Passivhaus is.

A cooling requirement, like a heating requirement, is dependent on the performance of the house. Part of Passivhaus is the 'fabric first' approach which delivers performance which massively lowers this requirement, in some cases eliminating it.

As already posted, ventilation solves the IAQ problem.

you dont seem to have read the article. passive houses generally have very good insulation, very air-tight envelopes and a system that is called heat recovery ventilation.

insulation and air tightness afford the house the property of staying the same temperature on the inside regardless of the temperature on the outside, more or less. if its too hot or too cold outside, this is something you always want. heat recovery ventilation gives the house the ability to move old air out of the building and new air into the building while not changing the temperature of the air inside, more or less. this is why its called heat recovery (also it could also be called cold recovery). this solves humidity problems.

the end result is a house that will tend to stay the same temperature, whether that is hot or cold. in an ideal model of this kind of house, you can see that heating and cooling costs are reduced to almost nothing because you simply choose a temperature that you like and simply never think about it again. this is the origin of the "passive" component of "passive house." with a passive house, you simply dont need a large hvac system. and there is nothing stopping you from adding a modest solar system to your passive house to get to net zero -- it is done quite frequently.

> insulation and air tightness afford the house the property of staying the same temperature on the inside regardless of the temperature on the outside, more or less.

But how is that initial temperature determined? If the house is built in a area during a time of year where the average air temperature is about 85F, then will the house always be too hot? How does it get cool (or hot) in first place?

the initial temperature, in that ideal system, is determined by deliberately making it hot or cold with a small sized air conditioner or heater. so in the ideal system you heat or cool once and then never again.

A common thing to do with a passive house is to put a bidirectional heat pump in the heat recovery ventilator. So you get cooling as well as efficient heating. With a passive house you only require a bit of either.

Climate dependent of course...

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