Why am I putting in an ashp in a passive house?

[Sparrowhawk]

6 hours ago, SteamyTea said:

All they had to do was explain brake specific fuel consumption, but that involves a tiny bit of physics and arithmetic, so scares off 95% of the British, who prefer their own small world view of 'I know for a fact as I have seen it with my own eyes'.  The limes v cement based render debate is a classic.

 

It the lime vs cement one here about flexibility, or breathibility?

[JohnMo]

48 minutes ago, Iceverge said:

€5500 A2W ASHP would save €950/year (5 year payback) . €550 total bill

Not sure you need to pay that

Samsung 5kW £1500 plus £350 for controller. All options need a basic cylinder. So now you are at 2 year payback

[SteamyTea]

1 hour ago, Sparrowhawk said:

 

It the lime vs cement one here about flexibility, or breathibility?

Don't really matter, I have not seen much genuine data about lime, ever, and very little on cement mixes.

[JohnMo]

2 hours ago, Sparrowhawk said:

lime vs cement one here about flexibility, or breathibility

Depends how you define breathability, water vapour or air.  Cement is a water vapour open structure the same as lime. Air breathable why would you want it?

 

Flexibility lime yes, cement and lime mix yes, cement only no.

[SteamyTea]

7 minutes ago, JohnMo said:

Flexibility lime yes, cement and lime mix yes, cement only no.

I have not seen any Young's Modulus numbers either way.

But this is derailing thing Heat Pump thread, which could become quite interesting.

[JohnMo]

I have come across these heat pumps. The first is rated a 3kW, it has a single outlet temperature set point. Not sure about modulation, its £1500.

https://eco-outlet.co.uk/products/activair-3kw-indoor-air-source-heat-pump

 

It sits indoors, so could be manipulated with air ducts to do cooling in summer and possibly take discharge air from the MVHR in winter, so zero defrosts. You may need to do a buffer, but no different from Jeremy and @joe90 did. Or if heating a thick slab, you could flow at the same set temperature as for DHW heating. Sounds daft, but a heat pump will manage dT first and dT is generally 5 to 6 degrees. So batch heating a floor would be as follows

 

Water exits floor at around 23 degs at start of batch charging, dT 6 applied so flow temp is pegged at 29 until floor takes some heat, temp would very slowly ramp up, floor taking 3kW. By the time it gets to 30 degs outlet a passivhaus thermostat would trip the unit off and it would move to DHW heating. I operate my UFH in a similar way (but set point is 35) and it never goes past 33.

 

The second unit is Cool Energy basic heat pump on eBay is 6kW unit, but control is similar to above but sits outside.

[joe90]

23 minutes ago, JohnMo said:

but no different from Jeremy and @joe90 did.

Yes we had the same ASHP, single outgoing temp (mine set to 48’ for DHW and buffer)  and blended down on the UFH manifold to 24’. (£850 on EBay)

[Simon R]

16 hours ago, Iceverge said:

For us I decided that an A2A HP and 4kW of PV would virtually eliminate bills. Time will tell.

We also went this route having decided that an ASHP was an overkill for a property that didn't require much more than 2kW heat input. We're into our second year and it has worked out very well for our place which is open plan as the one A2A unit takes care of the whole house for both winter and summer. Our annual consumption for the house was 538kWh last year which included cooking , lights etc BUT not hot water which is provided by a small combi boiler.

Installation cost less than 2K and it's a very comfortable way of heating and cooling. Considerably simpler than an ASHP and underfloor heating.

[Iceverge]

I have a thread somewhere where I've been monitoring our electricity usage. With the last 2 years. 

 

I'll have to update it again. 

 

 

[Iceverge]

13 hours ago, JohnMo said:

Or if heating a thick slab, you could flow at the same set temperature as for DHW heating. Sounds daft, but a heat pump will manage dT first and dT is generally 5 to 6 degrees. So batch heating a floor would be as follows

 

Water exits floor at around 23 degs at start of batch charging, dT 6 applied so flow temp is pegged at 29 until floor takes some heat, temp would very slowly ramp

 

I didn't realise that was how they worked. 

 

Essentially on a dT basis. 

 

I'm very much a fan of letting physics do the controlling rather than anything active.

 

 

[SteamyTea]

14 hours ago, JohnMo said:

Water exits floor at around 23 degs at start of batch charging, dT 6 applied so flow temp is pegged at 29 until floor takes some heat, temp would very slowly ramp up, floor taking 3kW. By the time it gets to 30 degs outlet a passivhaus thermostat would trip the unit off and it would move to DHW heating. I operate my UFH in a similar way (but set point is 35) and it never goes past 33.

 

15 minutes ago, Iceverge said:

Essentially on a dT basis. 

 

I'm very much a fan of letting physics do the controlling rather than anything active.

I am interested in how stable the room temperatures stay?

 

My old fashion storage heaters, in effect, work in a similar way to 'slab charging'.  The difference is they take a fixed amount of energy, over a fixed time.  This can cause, when we have very large temperature swings overnight, to change the room temperature.

It is a bit hard to know if it is just much warmer or colder air entering the house that has the greater effect, or the losses though the fabric.

Not really a problem as it is no more than 1.5°C either way.

[JohnMo]

56 minutes ago, SteamyTea said:

interested in how stable the room temperatures stay?

This is a sensor in the hall, had to go back in time to find a day not affected by solar gain. So get about 0.5 Deg fluctuation over a 24 hr period.

 

 

 

[SteamyTea]

3 minutes ago, JohnMo said:

This is a sensor in the hall, had to go back in time to find a day not affected by solar gain. So get about 0.5 Deg fluctuation over a 24 hr period.

 

 

 

I obviously don't have a room stat as such, just input and output stats are in the storage heater, but they are not brilliant for sensing actual room temperature.

 

It did cross my mind that as the ΔT decreases, the heat pump can modulate the power downwards a bit.

[JohnMo]

13 minutes ago, SteamyTea said:

did cross my mind that as the ΔT decreases, the heat pump can modulate the power downwards a bit.

The way mine seems to work is

 

Target temperature and dT

Starts up maintains dT first, as dT decreases over time, it add more heat to increase flow temp to maintain dT. Once target flow temp is reached, it reduces load (modulates down) to keep flow temp and dT within limits.

[JohnMo]

I have two shelly H&T's for monitoring, one in the hall the other in the garden room.

 

So comparison to the above post

Different type of building, summer house (200mm polystyrene floor and roof insulation, plus multifoil, with air gaps, 70mm thick wood walls with 140mm mineral wool insulation). Inside temperature profile, very different. Fan coil, thermally light weight building, heating goes off at midday.

All driven from the same heat pump as the house, this is yesterday and this morning, the big peak is solar gain. 3am fan coil starts up, with a flow temp that slowly ramps up to about 32/33 degs, takes 5 hrs to increase room temp from 12 to 20 degs., then maintains it till midday.  Once solar gain stops the heat drops around a degree per hour.  Outside temp at 5pm was about 5 degs and 10pm zero.

 

Yesterday house temps

Big dip in the blue was windows and doors open, we closed the door at 5pm and temp recovers quickly. But lounge window stays open for a further couple of hours. Bedroom was warm and we kept the window open all night (zero overnight outside).

 

[joth]

I worked on a PH project last year (south of England) where the clients decided against any heating and it's been on an ongoing effort to retrofit it ever since. They also based the decision on talking to other people that live in Passivhauses and claim they only turn on the heating twice a year. Be very wary of those sort of claims: the people making them are often highly invested (financially and emotionally) to push the performance of their building. Also just because one PH building does not need active heating it means nothing for the next.

 

ASHP is a bit of a red herring. The question is, do you need heating, and if so where and how much, and then ASHP is one possible solution to that.

 

What is the max heating load and annual heating demand in your PHPP model? This is key.  The project I mentioned before had a heating load of 3kW. This can be provided by a plugin 3kW heater - but then they baulked at having 3kW heater on 24/7 through the cold parts of winter (£25 per day). Mains gas or a heat pump are the options to reduce that cost.

 

[JohnMo]

1 hour ago, joth said:

and claim they only turn on the heating twice a year

Possibly don't qualify with when it got switched off. I only switch my heating on once a year, the same with cooling, then a thermostat does the rest.

 

1 hour ago, joth said:

heating load of 3kW

That's about the same as my non-passivhaus. I found heating our summer house with an 800W heat load expensive via a panel heater. So tied into the heat pump.

[ProDave]

4 hours ago, joth said:

I worked on a PH project last year (south of England) where the clients decided against any heating and it's been on an ongoing effort to retrofit it ever since. They also based the decision on talking to other people that live in Passivhauses and claim they only turn on the heating twice a year. Be very wary of those sort of claims: the people making them are often highly invested (financially and emotionally) to push the performance of their building. Also just because one PH building does not need active heating it means nothing for the next.

I often speculate how my house would perform if I just picked it up from here in the Highlands and put it down in say Cornwall close to the coast where frost is rare.  It would certainly be cheaper to run.  PHPP sets out a max heating requirement per square metre.  Does that account for location, i.e. to meet that a house up here would need more insulation than one in Cornwall?

[SteamyTea]

1 minute ago, ProDave said:

in say Cornwall close to the coast where frost is rare

We have had 2 frosts this winter.

How would you deal with the rain, we have had 2 days without any this winter.

[ProDave]

12 minutes ago, SteamyTea said:

We have had 2 frosts this winter.

How would you deal with the rain, we have had 2 days without any this winter.

Were they the frosty days?

 

That is why we chose not to move to the west coast.  Cold but dry is not so bad after all.

[Gone West]

27 minutes ago, ProDave said:

Does that account for location, i.e. to meet that a house up here would need more insulation than one in Cornwall?

Yes the PHPP requires comprehensive weather data for your locality. If the correct weather data isn't used it can have a large effect on the results. When I ran my house design through the PHPP I used four different sets of weather data to see the difference.

[SteamyTea]

26 minutes ago, ProDave said:

Were they the frosty days

Doubt it.

Just a thin film on the car windscreen.

There was snow once, it layed on the ground for a few hours.

 

I have just commented on the rain while buying a coffee.

Most of our rain comes when the West Indies is warm and has extra evaporation.

The Caribbean must be almost dry now, there cannot be much left.

[BotusBuild]

44 minutes ago, ProDave said:

we have had 2 days without any this winter.

Been great for leak detection 🙂

[tuftythesquirrel]

On 24/03/2024 at 16:10, JohnMo said:

Depends how you define breathability, water vapour or air.  Cement is a water vapour open structure the same as lime. Air breathable why would you want it?

 

Flexibility lime yes, cement and lime mix yes, cement only no.

 

Lime & Cement

I had a builder friend renovate part of our 450 year old house. He said he would use a lime & cement mix for the internal render, since he had been doing it "all his life". It failed and cracked in the time honoured tradition, so that you could see every one of the stone mortar joints under the render. When I susequently went on a lime building course at Ty Mawr Lime, Brecon, I relayed my experience. They said the mix was totally inappropriate and bound to fail. They also advised that the modulus of elasticity of the lime mix is some 400 times more flexible than good old cement. We removed it and re-rendered it with lime and it was perfect. Unfortunately, it seemed to me he had been doing it "all his life" wrong!

[Simon R]

13 hours ago, ProDave said:

I often speculate how my house would perform if I just picked it up from here in the Highlands and put it down in say Cornwall close to the coast where frost is rare.  It would certainly be cheaper to run.  PHPP sets out a max heating requirement per square metre.  Does that account for location, i.e. to meet that a house up here would need more insulation than one in Cornwall?

Your SAP calculations have a W/m2 and a W/structure per degree C values. Multiplying these by the HDD (Heating Degree Days) for your location or any other location will give you an idea of the annual energy cost.