How to heat and perhaps cool a passive type house

[PrincessB]

There was a great presentation at the Housebuilding and Renovation show last weekend. Subject was on building an Eco House, some of the decisions you'll need to make and the knock on effects of these decisions.

A knock on, for example, was the elimination of a heating system, barring the log burner (balanced flue type to aid airtightness of structure). It was pointed out that while this might work very well, should you need to sell the house, it can put buyers off when you tell them you've got no heating.

Second point was the use of a gas should it be available. The point in this case was that as many power stations burn gas to generate electricity which they then sell to you for several times more than gas, you might as well burn the stuff yourself.

They gave some of the positives of MVHR (Mechanical Ventilation with Heat Recovery) which for the most part needs to be designed and installed during the build phase rather than retrofitted - Which can be tricky. The alternative is trickle vents which lose you more energy and mean you can't get Passivhaus certification as there are too many holes in the structure.

As final points, we were told that with highly energy efficient houses, there can be more problems with overheating than ever being too cold.

To wrap up, another part of the talk was about the list you'll make which starts with the stuff you really need, such as a kitchen. Next step is the stuff you really want, such as solar panels or a Tesla and then designing want to can afford into the plans.

Having watched just about every housebuilding show out there over the last few years, the number of people who get all carried away and spend huge amounts on something that could be retrofitted (like the kitchen or solar panels) without budgeting to actually finish the house stand shoulder to shoulder with those who keep making changes as the build progresses.

The title question really asks it all, if you were considering a house that would be built to such energy usage standards, what would you install to heat and cool?

Regards,

B.

From a slightly earlier post, my cottage consumes about 100kWh (gas + electricity) per square metre of internal floor space. Passive houses aim for 10kWh per square metre.

[Urbandreamer]

I spent many decades considering the problem, and never got around to doing anything.

The first thing to consider is the orientation of the house. You NEED a south side. Having the long sides on east or west may make the most of the view when you get up or go to bed, but suck for thermal gain.

Some form of awning over the windows is a MUST for me. To explain, the sun is low in winter when you want thermal gain and high in summer when you don't. Awnings keep the summer sun out while allowing the winter sun in. I'm using the word awning, but you may recognise the concept of a verander with a roof. Or a pergola, with plants that shed in winter. They achieve the same effect.

Do your insolation charts and calculations. (Yes that was in-sol-ation, what sun you get)

Smaller windows, if any on the north and blinds, shutters AND curtains. Windows are very significant in terms of heat loss.

Very well insulated walls and roof. If possible insulated on the outside, or at least with most thermal mass inside the insulation.

Modest rather than high thermal mass (concrete, bricks or tanks of water). Where we live it's likely that a fully passive house isn't going to be possible. Hence being able to raise the temperature a couple of degree's quickly will make for more comfort than having a large thermal store that takes significant time to lose or gain heat.

Tiled solid floor down stairs, to take heat from the sun.

A south facing "green house" with a opaque roof and a Trombe wall with active vents would seem a good idea. You can have high thermal mass in the green house as you can choose to use stored heat or isolate it while you add heat to the living areas.

I wasn't a fan of active ventilation, but have changed my mind. In simple terms retrofits and early designed didn't work well. The mistakes have been made and the lessons learned I think.

[UncleEbenezer]

A couple of thoughts ...

I consider good ventilation essential. Give me fresh air and my body regulates its own temperature - that's precisely the ability warm-blooded creatures have that distinguishes us from our cold-blooded counterparts. Breathing stuffy air slows the metabolism and impairs our heat-regulation, causing us to feel much colder. If you feel the need to set the thermostat anything much over 12 degrees, you're doing something wrong.

Also watch your humidity. Dryer air, like fresher air, helps with feeling comfortable over a much wider temperature range (both summer heat and winter cold). And dryer air takes less energy to heat (or cool) than humid air.

Considerations like orientation and window sizes seem to me detached from reality for the majority who have to make lots of compromises over our housing. I have a north-south orientation, but the south side is overshadowed by a high bank, hillside and trees, meaning the river-facing north side is where I get most natural light and my two really nice rooms. In a previous home, I had an opposite problem: great south-facing windows that caught the sun's heat, but also faced too much town noise[1] so I had to escape them. Never mind every house, every site where a house might be sited has its own characteristics that have to be worked with.

[1] Notably a pub that specialised in the kind of band that makes up in decibels what it lacks in talent.

[todthedog]

A couple of recommendations
A sustainability forum, where folk have gone down the road and are happy to offer advise. There are several self build journeys, and retrofit improvements. Many of the topics you raise are covered.

Disclaimer I post on this site

https://www.navitron.org.uk/forum/index.php

This blog covers the life of a self build 'accidental' crofter

https://lifeattheendoftheroad.wordpress.com/

Best of luck

[Urbandreamer]

Considerations like orientation and window sizes seem to me detached from reality for the majority who have to make lots of compromises over our housing.

The concept of a "passive type house" is that little or no "activity" is required to make the house comfortable. Hence in cooler climates as much as possible of the heat should be provided by the sun shining in. In hot climates as much of the cooling should be provided by preventing the sun shining in and usually by capturing ventilation. Ie louvre plantation shutters, needed before air-con in certain parts of the world. They prevent the sun shining in but allow maximum ventilation.

passive heating
https://en.wikipedia.org/wiki/Passive_s ... ing_design
passive cooling
https://en.wikipedia.org/wiki/Passive_cooling

There are a lot of older houses where I live that are at odd orientations to the road. They had a lot of windows, though many now have stone infill. If you consider the orientation you will see that it is based upon the sun. They are known as weavers cottages and were built the way that they were for functional reasons.

Some might like this quote.

"Now, supposing a house to have a southern aspect, sunshine during winter will steal in under the verandah, but in summer, when the sun traverses a path right over our heads, the roof will afford an agreeable shade, will it not?" Socrates

Possibly, just possibly, something to think about when building a house?

[dspp]

I think you will find you are awry on your Passivhaus requirement, you state 10kWh/yr/m2. Below is the https://en.wikipedia.org/wiki/Passive_house requirement :

*******
The Passivhaus standard requires that the building fulfills the following requirements:[32][33]

Use up to 15 kWh/m2 (4,755 BTU/sq ft; 5.017 MJ/sq ft) per year for heating and cooling as calculated by the Passivhaus Planning Package, or a peak heat load of 10 W/m2 (1.2 hp/1000 sq ft), based on local climate data.
Use up to 60 kWh/m2 (19,020 BTU/sq ft; 20.07 MJ/sq ft) per year primary energy (for heating, hot water and electricity).
*****

So that is 15+60 = 75kWh/yr/m2 primary energy. For some reason I have it down as 120 in my other notes, but hey ho.

My primary energy actuals on a total area basis are 108 kWh/yr/m2, and on a habitable basis are 135kWh/yr/m2 so getting quite close and I have quite a lot left to do on a few cold rooms. Mine are a Victoria terrace N-S ridge (E-W orientation). Bottom line in my view is you can get a long way on a UK retrofit just by internal insulation (to minimise winter heat) and bris solaire (to minimise summer cooling) and careful electrical thinking. (My actual energy totals are lower still, but one must convert to primary energy to do the sums properly. Whoever is commenting on the gas/elec point has not done that piece of the sums as converting to primary takes that into account).

regards, dspp

[PrincessB]

Thanks to all for the responses, the different opinions expressed are especially welcome because by its nature the Lemonfool site is very general and to me the varied responses are more insightful than replies from the converts on an eco build site.

Not that I've got any issues with those websites and discussion areas, when one is trying to focus on the bigger picture, getting bogged down in the details can be less helpful than the input you've provided.

I'd like to thank, dspp for the link to the mechanics of the Passivhaus requirement and among the various statistics, this one really amused me.

or a peak heat load of 10 W/m2 (1.2 hp/1000 sq ft), based on local climate data.

There is a huge focus within the requirements to seal up the house like a drum and then have it tested by blowing air in through the door to ensure that nothing gets in and nothing gets out - This sounds expensive.

Then they add to the fun by by saying theres a limit to the power of the heater you can put in before they let you pass their special test for certification.

So my 120 m2 cottage should have at maximum 1200W of heating for the whole structure.

Bizarrely, the central heating packed up in here a couple of weeks ago, not the cold sub zero tempertures from the last few days, more like +5º (averaged over the day). The downstairs bathroom has a 1kW electric wall heater, so we turned it on and left the door open. With just that, the spare heat from the cooker and the occasional use of the gas fire in the TV room we were fine till it was fixed.

However, I did mess up the calculations for the radiators in the main kitchen diner area and when we spend a few days away in winter the temperature has dropped as low as 14ºC (I usually set heating to full on, hot water off and set the main stat to 10ºC to avoid problems.

On full power from the gas boiler, I should have about 3kW of heating in a room that when warmed up does not struggle to heat to 22ºC when it is -5ºC outside.

When it comes to warming up from low temperature, it takes hours to even take the edge off and there's not a lot of thermal mass in that part of the building. I can only assume passive means never ever turning the ventilation and minimal heating systems off which sounds like a made up of set of rules.

I've heard many people who build to these standards also include a log burner (which apparently breaks a few standards) I'm not sure how much they want you to suffer without a local source of high intensity heats, but I'm not convinced.

There must be a comedy skit worth writing about the folk with a passivehaus who return home after a holiday over winter and dig from various secret locations fan heaters in order to get the house warm in a reasonable time rather than the ones dictated by the standards set down by the rules.

Add in the stuff about not having and windows to speak of and I wonder who actually wants to build to that standard at all?

[PhaseThree]

I've just completed a passive spec house build in Northern Ireland. The House is around 270m2 and is heated by E7 electicity. Currently with the temperature outside somewhere between 0C - 5C we are using around 1kW to heat the place. The heating system is UFH fed from a small tank fitted with a 3kW immersion heater fed by E7. This heats the house slab to around 20C overnight. The slab stores enough heat to keep the house warm for the whole of the next day. In effect the slab is acting like a very large low temperature storage heater.

I have plumbed the build to allow me to install an ASHP at a later date should I need one for either heating or cooling (An ASHP can be run in reverse to cool the slab if required.). I have also wired the place to allow electic pannel heaters to be installed if required. To be honest the last few very cold nights have left the bedrooms feeling a bit cold so this may happen sooner rather than later.

Putting a wood burner into a house built to passive-ish specs is difficult. Even with the smallest room sealed version available (~4kW) the room will rapidly overheat, quickly followed by the rest of the house.

As a practical point I would caution against overdoing the heating, you will be supprised at how little you may actually need if you insulate and get airtightness to passive specs. A better solution is to install the heating components you cant easily retrofit (Pipes for heat pumps, cables for heaters and PV systems etc), then live in it for a year and decide what you actually need,

[dspp]

Thanks to all for the responses, the different opinions expressed are especially welcome because by its nature the Lemonfool site is very general and to me the varied responses are more insightful than replies from the converts on an eco build site.
......

There is a huge focus within the requirements to seal up the house like a drum and then have it tested by blowing air in through the door to ensure that nothing gets in and nothing gets out - This sounds expensive.

1. You can ignore certification unless a) you want to 'brand' your house as Passivhaus on resale or b) you don't know what you are doing design-wise and you need the stick of certification to avoid mistakes.

2. Don't laugh at the airtightness specs. They are there for very good reasons. Basically you want to heat/cool the air the humans are living in, not the air that is escaping outside. Forget the memes about living in a cold gale being good for you. But when sealing up you do need to get the right amount of airflow (hence the heat exchanger mechanical ventialtion systems in many passivhaus desgns).

3. The reason for doing the airflow test (and the reason the test is included in the certification) is to find out whether the builder/designer/vendor has done the job correctly before you pay them. You wouldn't pay an electrician unless they'd done the tests required to sign off the part P, so why treat passivhaus any differently ?

4. You can go a heck of a long way towards passivhaus, without making a big fuss about it, even on retrofits. In many ways that is the right thing for the oldbuild UK building stock to be doing. And in my view passivhaus should be mandatory for all newbuild UK buildings of all types.

regards, dspp

[todthedog]

Dspp is spot on you can go a long way down the road to a passive house without the certification.

Retrofit passive is extremely difficult to achieve.

I think you need to ask yourself 'what am I trying to achieve'

A comfortable environment for my family or something else?
Is cost a parameter?
Am I planning to be self sufficient in energy?
What is possible for my budget?
What are my priorities?

Air tightness is a must if you are taking the high insulation route on a retrofit .

Good luck

[88V8]

The obsession with energy use and consequent elimination of 'draughts' concerns me.

When I consider the huge rise in allergies, perhaps some of this is parents inflicting crackpot diets on their children, or parents' disinclination to cook from fresh, or perhaps the excessive use of Caesarian birth, but I cannot help suspecting that a lot of it has to do with houses sealed up tight as a drum, no 'draughts', no open chimneys, full of plastics and artificial fibres and household chemicals all of which give off detrimental emanations in varying degrees.

We as a species were not meant to live like that.

Last year I had some new windows made, repros for our C17 cottage.
They came with plastic perimeter seals. I was not pleased. He mumbled about FENSA. Eventually I shall replace the plastic with strips of wood, but for the moment I have removed a quarter of the seal from each window to ensure a decent 'draught'.

My wife and I have always lived in 'draughty' houses, with chimneys, heated to about 60F. We have no allergies.*

Just an observation.

V8

*although after catching a tropical illness I did go through a period during which I was allergic to while chocolate and Pernod, fortunately I made a full recovery.

[todthedog]

Sealed highly insulated houses probably have more ventilation than draughty ones. Warm damp air is typically taken from kitchen and bathroom, the heat in it is extracted (heat exchanger) to fresh clean air being drawn in from outside and warmed dry air filtered typically distributed to bedrooms.
If done properly producing a healthy living environment.

[staffordian]

The obsession with energy use and consequent elimination of 'draughts' concerns me.

When I consider the huge rise in allergies, perhaps some of this is parents inflicting crackpot diets on their children, or parents' disinclination to cook from fresh, or perhaps the excessive use of Caesarian birth, but I cannot help suspecting that a lot of it has to do with houses sealed up tight as a drum, no 'draughts', no open chimneys, full of plastics and artificial fibres and household chemicals all of which give off detrimental emanations in varying degrees.

We as a species were not meant to live like that.

Last year I had some new windows made, repros for our C17 cottage.
They came with plastic perimeter seals. I was not pleased. He mumbled about FENSA. Eventually I shall replace the plastic with strips of wood, but for the moment I have removed a quarter of the seal from each window to ensure a decent 'draught'.

My wife and I have always lived in 'draughty' houses, with chimneys, heated to about 60F. We have no allergies.*

Just an observation.

V8

*although after catching a tropical illness I did go through a period during which I was allergic to while chocolate and Pernod, fortunately I made a full recovery.

I'm convinced the key reason for the rise in allergies, asthma etc is due in large part to two factors. Pollution, especially small particulates, and the obsession with "killing germs". This latter fad will inevitably reduce immunities because the normal day to day interaction with microorganisms etc, which the body needs to learn to deal with are largely absent.

But I digress. Sorry.

[PhaseThree]

As part of our passive spec house build we sealed every conceivable air leak in the place - This is relatively easy to do at the first fix stage. As expected this led to a very stuffy and unhealthy house at this stage of the build. We then installed a ventilation system (MVHR - Mechanical ventilation with heat recovery) with dedicated supply and extract vents distributed around the house. The end result is a house with warm fresh air that is of a quality pretty much equivalent to having the windows wide open (I use a dedicated CO2 meter to measure air quality). The air is a lot fresher than we get in our old house (a leaky early 1980s build).
Clearly running a ventilation system 24/7 requires energy in itself so why bother ? The answer is that in a standard house around 1/3 of all heating energy disappears in "unintended ventilation". Sealing the house and using a MVHR greatly reduces the amount of heat lost hence saving energy while improving the ventilation.