"Upside down" EnerPHit project in N Devon

[DInwood]

Hello all,

I've been finding your experiences and wealth of knowledge fantastic during the fantasy phase of our project - thank you - but now it is getting real I was hoping for some more specific guidance.

We've bought a 1970s chalet/bungalow in north Devon and will be converting and extending it to provide a zero net energy home to retire to.  It is on a NE sloping site and will have living spaces & main bedroom on the 1st floor (with 3 more on GF).  Our architect has produced some great plans for about 165 sqm and the 1st pass of the PHPP says it will just about meet the EnerPHit standard.  The calculations indicate that a couple of small radiators and a towel rail attached to an ASHP will be enough, but I have read enough on this forum to believe that UFH will be better.  However I'm a little concerned whether our inverted arrangement affects this: with a concrete slab on the ground floor and the bulk of the thermal mass in the original GF walls, does this affect the logic of the heating plan?  (The GF will not be much used unless the kids & grandkids are visiting).  Also, how do you control the system to distribute heat/coolth around?

Thanks in advance for any input.

[joth]

Welcome! 

I'm interested to hear about your project, firstly becuae we're currently mid-build on an EnerPHit renovation (in Herts) but second, my wife and I are from N. Devon and lots of family still there. On the off chance you're in Barnstaple, I think I can make a good guess whereabouts! There's a whole street of NE-facing upside houses that I know quite well.

Impressed to hear you have an architect with PHPP knowledge! (Assume it was the architect that did the modeling?). 

 

In our project we're also going for ground-floor only UFH, largely based on what I learnt here. A large part of this is that we prefer slightly cooler bedroom than living rooms, so that works itself out naturally. The key thing of a well insulated and airtight house is, unless it's a really odd shape, it naturally converges to all rooms within the envolpe being similar temperature, as it's much easier for heat to move between rooms than escape the house, vs a traditional build. (Hence latest building regs requiring separate zone controls per room is rather misguided in a near-zero energy home; fabric first design often allows for less dependency on technical "work arounds" like this). 

 

The first thing I'd think about in an upside down house is what the ground floor is currently constructed of, and how much you're already planning to do to remove and replace it regardless of doing the UFH. For us, the desire to do UFH there drove the decision to replace and insulate the concrete slab, which in turn enabled the decision to go for EnerPhit. If the house was the otherway up we might have made some different value choices which could have led to a very different projects.

(BTW we also considered demolish and rebuild, largely because the VAT savings that brings would pretty much pay for the additional work, and if we had done that we'd have been very tempted to propose and upside down design. The main reason we went with renovation was expediency in getting the project underway).

 

 

[A_L]

hello and welcome,

 

I would heat the GF with UFH if you want.  This would reduce the heat-loss of the first floor to a point where a post heater in the ducting of the MVHR to the first floor could easily cope with the first floor heat demand.

[Omnibuswoman]

Hi Dinwood,

We are in a very similar position - likely reverse living house on the Devon/Cornwall border, aiming for PH or close to it, and will have UFH on ground floor only. I was wondering whether we would need anything further on the first floor too, so am glad of your question and the answers above.

 

@A_L, I didn’t quite understand what you said about ‘where a post heater in the ducting of the MVHR to the first floor could easily cope with first floor heat demand’. Would you mind unpacking that a bit for me please??

Cheers

M

[BotusBuild]

A post heater fits inline after the MVHR unit in the "air into the house" ducting (supply ducting). So "post" as in "after" as opposed to "pre" as in "before".

 

The post heater adds a little extra heat if required to the incoming air.

 

So the air flow would be from the outside:-

OUTSIDE AIR -> DUCT -> MVHR -> POST HEATER -> DUCTING INTO HOUSE

Edited June 8, 2020 by BotusBuild

[Omnibuswoman]

Thanks @BotusBuild! That makes perfect sense.

[SteamyTea]

If you are considering UFH, how much insulation are you going to fit under it. Heat loss to the ground is greater with UFH than radiators or forced air systems.

If you fit post heating to your MVHR, chech that the airflow is large enough to transfer enough energy. It is easy to put in larger ducts at the design stage.

You mentioned 'thermal mass'.

This is a contentious term and has no basis in science.

What you actually mean is thermal inertia, which is the product of the specific heat capacity and the thermal conductivity.

What that boils down to is the time it takes for the air in the house to drop by 1°C when there is no extra energy input i.e no heating.

Brick and concrete are not very good, timber and cellulose insulation are very good.

Edited June 8, 2020 by SteamyTea

[DInwood]

Thanks to all for your input.  I'm grateful to SteamyTea for the terminological correction and the re-education; I had believed that the heat capacity of the original walls (GF only) and new highly insulated GF slab would act as a store and also a sink for when the 1st floor overheats (most of the solar gain is from the 1st floor SW glass).  If the inertia of timber & cellulose are better, then they are more significant on the 1st floor, so good news?

If we are putting in UFH in the GF, is there much incremental cost in adding in the 1st floor (probably bamboo flooring)?  I've read many times on this forum that moving heat from areas with high solar gain is one of the main benefits.

What would be the energy source for a post heater in the 1st floor MVHR?

Joth, not Barnstaple but Appledore - close!  The decision to replace the original suspended floor was made to meet EnerPHit performance I believe. 

I could have a whole different conversation about finding an architect for a "zero carbon" project... but we are very happy with our eventual choice.

Regarding VAT, we have been advised that we qualify for reduced rate as the house will have been empty for years when the works eventually start.

Could I repeat my question about heating controls?  I can't picture how the running of the UFH pump, demand for heat or switch to cooling are all controlled and what constraints it puts on the choice of ASHP.

[SteamyTea]

59 minutes ago, DInwood said:

What would be the energy source for a post heater in the 1st floor MVHR?

Basically you have a choice of two systems.  An electrical, in line, resistance heating element, or a fluid filled 'radiator'.

The electrical one is easy, it just plugs into the mains, the other is then really up to you how you heat the fluid.  But if you are using an ASHP to heat your domestic hot water, it can be 'tapped' off that system.  Some MVHRs (Genex for one) have a build in heat pump to add to heating and cooling.

59 minutes ago, DInwood said:

Could I repeat my question about heating controls?  I can't picture how the running of the UFH pump, demand for heat or switch to cooling are all controlled and what constraints it puts on the choice of ASHP.

This is really two questions.  How does a heat pump work in practice? and what is the best way to control the complete system?

At its most basic, a heat pump has a hot side and a cold side.  The plumbing within the heat pump will control which side is piped into the house.  Basically there is the refrigerant pump, then, via some heat exhangers, some pipework to a radiator (the air source bit) that is outside, and some pipework to inside the house (the source or sink) for space and\or water heating.  Just a case, depending on what you want, as to how the control valves reconfigure the heat exchangers.

 

As for the house heating controls, this is a bit more complicated as it is very much dependant on the shape of the house and the usage.

It is usual to zone areas and control each zone separately.  That way you can have different temperatures, at different times for heating or cooling, is on and in different places.

What many have found though it that having just one zone for the whole house is often good enough, and can be used to move excess heat around if needed, without using the heat pump (just pump the water in the UFH about).

 

One thing with heat pumps is that they need to be designed correctly for the expected heat loads.  This usually means over sizing them as that keeps the coefficient of performance up.  Most modern ASHP have variable speed motors in them that accommodate this.

It is also worth getting to grips with the difference between temperature, power and energy.  They are not the same thing.  You can have high temperature, but low energy and low power, low temperature and high energy and power, high or low power, medium energy and variable temperature.

All a juggling game.

Edited June 9, 2020 by SteamyTea

[joth]

1 hour ago, DInwood said:

Joth, not Barnstaple but Appledore - close

Oh my, my real ancestral home (although never lived there myself) got relations going back for generations there on all sides of the family. Although of course mostly moved out to make way for all the holiday/second homes. 

Reminds me, Hockings just restarted trading so I must make a pilgrimage to acquire a 4L tub for the summer as soon as I can :-)

 

1 hour ago, DInwood said:

Regarding VAT, we have been advised that we qualify for reduced rate as the house will have been empty for years when the works eventually start.

 

Ah good stuff. Only after we moved into our house (invalidating the 'empty clause) did we discover it had been empty for several years, not the 12 months we were told when buying. Couple quick things to be aware of:

- you need evidence of continuous unoccupied status. e.g. council tax exception letters are pretty good.

- you mustn't do anything to invalidate that unoccupied status, right through until the day your contractor(s) start.

- IIRC the VAT discount only applies to the bills (materials + labour) from contactors, not for any materials you buy to install yourself. 

 

But if you can make all that work, it will be well worth it.

 

 

[MrMagic]

Love a good Hockings. Wifes family is from the area and we're usually down in Braddick Land (WWHO) a few times a year, was at the Appledore carnival last year. Small world eh?

 

Ask 100 people a question and you will get 100 different answers - my one to throw in to the ring would be why spend many thousands on an ASHP when you could sperate DHW and CH. Use 3 or 4 air2air heat pumps (air con units) internally to cover your bedrooms and downstairs areas and go with either a vented or unvented DHW cylinder (or even better a Sunamp). Far more control and flexibility Vs big old radiators + cooling in summer.

 

[A_L]

1 hour ago, DInwood said:

What would be the energy source for a post heater in the 1st floor MVHR?

 

Usually electricity but wet in-duct heaters are available, normally gas fired, distribution temperatures can be quite high so ASHP may not suitable.

 

1 hour ago, DInwood said:

I had believed that the heat capacity of the original walls (GF only) and new highly insulated GF slab would act as a store and also a sink for when the 1st floor overheats

 

It will act as a store but since heat rises probably not as a sink for when the 1st floor overheats. It would require active movement of the heat to the ground floor.

 

1 hour ago, DInwood said:

If the inertia of timber & cellulose are better, then they are more significant on the 1st floor, so good news?

 

Stepping where angels ................?

 

Cellulose and timber do have higher specific heat capacities 2100J/kg.°C and 1600J/kg.°C than Brick, 500J/kg.°C and Concrete, 750J/kg.°C but the greater density of these, 1750kg/m³   and 2300kg/m³ compared to 40kg/m³ and 500kg/m³ means that they store more heat on a volumetric basis. Concrete 1725kJ/m³, Brick 1400kJ/m³, Timber 800kJ/m³ Cellulose 84kJ/m³ 

[SteamyTea]

58 minutes ago, A_L said:

Cellulose and timber do have higher specific heat capacities 2100J/kg.°C and 1600J/kg.°C than Brick, 500J/kg.°C and Concrete, 750J/kg.°C but the greater density of these, 1750kg/m³   and 2300kg/m³ compared to 40kg/m³ and 500kg/m³ means that they store more heat on a volumetric basis. Concrete 1725kJ/m³, Brick 1400kJ/m³, Timber 800kJ/m³ Cellulose 84kJ/m³ 

The volume becomes a bit irrelevant when the temperature changes are only affecting the first few millimetres.

This is why it is the product of the SHC AND thermal conductivity..

There are materials that have low SHC and high thermal conductivity, metals being one class, but there are not many materials that have high SHC and low thermal conductivity.

Below is the data from my 600mm borehole that is under my little grrenhouse.

Once you are 300mm deep, there is little variation in temperature, approx 5°C, with temperature swings of 32°C within the greenhouse.

This reinforces my believe that excess mass with the 'wrong' thermal inertia will cause cooling rather than stability.

 

 

[A_L]

17 hours ago, SteamyTea said:

The volume becomes a bit irrelevant when the temperature changes are only affecting the first few millimetres.

This is why it is the product of the SHC AND thermal conductivity..

 

The products (J/kg.K x W/m.K) are Cellulose 84, Timber 208, Brick 280 and Concrete 1350.

 

17 hours ago, SteamyTea said:

This reinforces my believe that excess mass with the 'wrong' thermal inertia will cause cooling rather than stability.

 

What is the energy source to drive this cooling and where does the energy go?

[SteamyTea]

14 minutes ago, A_L said:

What is the energy source to drive this cooling and where does the energy go?

The energy source can be anything, heating, lighting, solar gain, people.  The energy is just dispersed to the atmosphere, which is generally colder, or, for the proper scientific term, a semi-infinite heat sink.

Edited June 10, 2020 by SteamyTea

[ProDave]

Just my obbservations with a near passive house and heating only on one floor.

 

We only heat the downstairs with UFH and the room thermostats set to 20 degrees.  In the depths of winter, the upstairs bedrooms get down to about 18 degrees.  We find this just acceptable.

 

Swap the rooms around and you would have unecessarilly hot bedrooms and a living room that was too cold.

 

So you will want some (not very much) heating in the upstairs living space. That would allow you to run the downstairs (bedroom) heating lower.

 

I can't see a scenario where you can only heat one floor.  If you only heat the upstairs, then there is a good chance the bedrooms would get too cold.

 

 

[SteamyTea]

22 minutes ago, ProDave said:

I can't see a scenario where you can only heat one floor.  If you only heat the upstairs, then there is a good chance the bedrooms would get too cold.

It may be possible to utilise the MVHR to extract air from the living area and deliver it to the sleeping areas. There may be enough of a temperature drop to deliver the fresh air at an acceptable temperature.

You would still need to introduce fresh air to the living area, and extract from the sleeping area, but this may just be a case if adding two inputs to the sleeping area for every one extract, and visa versa in the living area.

Should not be too hard to calculate.