New build - heat and energy considerations

[Guest Alphonsox]

I don't have full running costs as yet, still gathering data. I run the heating on E7 electricity, the immersion runs for a maximum of 7hrs @ 3Kw, (so 21kWh/day maximum). In reality the immersion is typically on for a small portion of the available 7hours.. The slab works as a very large storage heater and seems to happily heat the whole house around the clock.

The DHW is completely separate and runs from a couple of SunAmp units also heated from off-peak E7 electricity.

I bought the ASHPs for an extremely good price when Kingspan got out if the business. The idea was to install one and keep the other for parts. This was before I realised how little energy a Pasiv-ish spec house requires for heating. I may still install one but the cost of the glycol to fill the system would be enough to heat the place for a good few years.

[Jimbouk]

Tyke2 I relate to your adverse experience of ‘eco’ commercial buildings. I have enjoyed operating a number of Bream ‘very good’ designed by award chasing architects, then specified by value engineeers. Not a pleasant experience for the wallet! 

 

I vowed that that my build would be ultra simple, however I have ended up with ufh, mvhr and passive inspired design.

 

The difference is that this time I am (vaguely) in control of the specifying and can directly equate to the benefits I hope to experience over future decades. I’m not procuring my solutions from the cheapest suppliers of obsolete or unproven products, nor am I buying cheap solutions with backend loaded maintenance contracts / Warranties.

 

I would echo the keep the control side simple, I’m astonished at how little heat (and in turn control required) says the man with 8 zones....

 

 

Edited September 10, 2018 by Jimbouk

[joe90]

An ASHP is basically a fridge running in reverse, how often do you service your fridge? UFH is pipes buried in concrete, what can go wrong?. MVHR is two low energy fans and a radiator and some simple electronics.  my build is fabric first and attention to detail (overseen or done by myself). Insulation is fairly cheap and you buy it once , fossil fuels cost endlessly plus price rises. I too like uncomplicated systems (I am a Luddite by nature?)  I only have electric UFH in our en suite and electric towel radiator upstairs, I believe heat will rise from downstairs to heat upstairs enough, if not (very cold snap in winter) a couple of low wattage electric fan heaters will be more than enough to cope. I am contemplating E7 or E10 but will need to see how the house behaves for a year to see if it’s required. Read, read and read more on this forum and you will be enlightened.

[Ed Davies]

11 hours ago, joe90 said:

how often do you service your fridge?

Also, how many fridges are chucked out because the heat-pump part failed? A few, but not many and most likely because they get noisy rather than outright fail. Mostly people get rid of them because the insulation or seals fail and they get grotty, or they're a bit old and not fitted into a wider kitchen refresh/upgrade.

[Tyke2]

11 hours ago, joe90 said:

An ASHP is basically a fridge running in reverse, how often do you service your fridge? UFH is pipes buried in concrete, what can go wrong?. MVHR is two low energy fans and a radiator and some simple electronics.  my build is fabric first and attention to detail (overseen or done by myself). Insulation is fairly cheap and you buy it once , fossil fuels cost endlessly plus price rises. I too like uncomplicated systems (I am a Luddite by nature?)  I only have electric UFH in our en suite and electric towel radiator upstairs, I believe heat will rise from downstairs to heat upstairs enough, if not (very cold snap in winter) a couple of low wattage electric fan heaters will be more than enough to cope. I am contemplating E7 or E10 but will need to see how the house behaves for a year to see if it’s required. Read, read and read more on this forum and you will be enlightened.

Hi Joe90

 

Thanks.

I'm 100% in favour of fabric first. I doubled up on insulation on my last build, the cost was minimal.

For the electric UFH - does this have a high energy usage? Is it electric matting or electrically heated wet system?

I hope you are correct on the issue of the heat rising upstairs. I am aware that one of the companies I worked for did a UFH downstairs and radiators upstairs. I was not involved but am told the radiators with TRV's never actually came on, so you may be correct.

I have installed an electric wet system using E10 , but again back in 2000 when smart meters were not in use. The E10 was very difficult to get sorted, hopefully it is easier now.

I would be interested what actual the electricity usage is on yours, if the temp is kept during normal hours at a comfortable temperature, e.g. 22 to 24 Celsius.

 

[Tyke2]

5 minutes ago, Ed Davies said:

Also, how many fridges are chucked out because the heat-pump part failed? A few, but not many and most likely because they get noisy rather than outright fail. Mostly people get rid of them because the insulation or seals fail and they get grotty, or they're a bit old and not fitted into a wider kitchen refresh/upgrade.

I'm pretty sure a noisy heat pump/fan on the HP would be changed similarly? 

[Stones]

@Tyke2 bearing in mind that building regs require a pretty decent level of insulation anyway, if you pay attention to the airtightness detailing, your heat demand isn't going to be huge, and may well be less than your DHW.  We have an ASHP and it works really well via UFH, keeps the house warm and at a very stable and comfortable temp for very little cost.  You could achieve the same with a simple direct electric system (Willis heater) at a higher running but lower capital cost.  Radiators can work with a low temp system - we had such a system in our last house but radiator sizes are massive and resemble armour plating on a dreadnought.  If you just want small high temp radiators you start adding complication to your system (and potentially higher running costs of usung an ASHP as COP drops as output temp rises) Better avoided if you can in my view. 

 

Various ways you can deliver DHW, from simple immersion (low capital but higher running cost) to ASHP only or a mix of the two.   When I costed it out, I calculated it would cost the same to preheat DHW with an ASHP then top up with immersion vs ASHP only heated to 50C.  I went with the latter for simplicity and it works really well (the most recent entry in my blog gives some details on this). 

 

 

 

 

 

 

 

[joe90]

31 minutes ago, Tyke2 said:

Hi Joe90

 

Thanks.

I'm 100% in favour of fabric first. I doubled up on insulation on my last build, the cost was minimal.

For the electric UFH - does this have a high energy usage? Is it electric matting or electrically heated wet system?

I hope you are correct on the issue of the heat rising upstairs. I am aware that one of the companies I worked for did a UFH downstairs and radiators upstairs. I was not involved but am told the radiators with TRV's never actually came on, so you may be correct.

I have installed an electric wet system using E10 , but again back in 2000 when smart meters were not in use. The E10 was very difficult to get sorted, hopefully it is easier now.

I would be interested what actual the electricity usage is on yours, if the temp is kept during normal hours at a comfortable temperature, e.g. 22 to 24 Celsius.

 

 

Hi Tyke2, we have only just moved in so I am unable to give examples of electricity usage. Our ensuite is electric wire embedded in self levelling compound with QVT on top run by timer and thermostat , towel radiator is 300 watt (was 700watt but got too hot) also run by timer. The UFH downstairs is wet run from an ASHP which will also deliver DHW to a 300litre insulated tank.

 

 

 

Unlike so many on this forum I used gessanometry to work out what was required, others have used software such as PHPP . We also have a room sealed Wood burning stove in the lounge which many on here says will overheat the house but with bifolds into a large sunspace (eco word for conservatory ) I don’t think it will be a problem. We are looking forward to winter evenings watching the stove rather than a lot of crap on TV. (Note, a lot on here are against wood burning stoves but we are in a remote rural location with a source of wood so am happy with our decision).

 

We have no trickle vents but have MVHR to recover most of the heat from our ventilation requirement, this also saves us having kitchen and bathroom extractors which are big thermal bridges.

 

With no access to mains Gas I believe electric using an ASHP is the best option plus the fact we have no standing charge for Gas connection and annual service charges. As I said above we will need to see what our usage pattern is and see if E7 or E10 is worthwhile.

 

whatever our usage is it will be far less than a “normal” house

 

 

 

 

Edited September 11, 2018 by joe90

[joe90]

10 minutes ago, Stones said:

When I costed it out, I calculated it would cost the same to preheat DHW with an ASHP then top up with immersion vs ASHP only heated to 50C.  I went with the latter for simplicity and it works really well (the most recent entry in my blog gives some details on this).

 

I forget who it was but someone slowly raised their DHW temp to the point where they could only just hold their hand under the tap and measured the temp at 47’. Raising the temp higher only just wastes energy (IMO).

[Ed Davies]

31 minutes ago, Tyke2 said:

I'm pretty sure a noisy heat pump/fan on the HP would be changed similarly? 

Nobody changes the pump on a fridge. Similarly, I'm not sure whether people change the pump on an ASHP because of the restrictions on the refrigerants. Still, the fan should be an easy change.

 

I expect to own two fridges in my life. The one I bought in my early twenties which I chucked when I sold my old house in my mid fifties (because it was very grotty and a bit noisy) and the one I'll buy when I move into my completed house which I expect will outlive me. I don't see why ASHPs shouldn't be a similar deal.

[Ed Davies]

4 minutes ago, joe90 said:

I forget who it was but someone slowly raised their DHW temp to the point where they could only just hold their hand under the tap and measured the temp at 47’.

Yes, the usually reckoned highest temperature for washing up is 48 °C. Assuming that's the temperature out of the tap then the water in the bowl will be a tad cooler which matches perfectly. A shower's about 38 °C. Other washing somewhere in between.

[Tyke2]

Not relevant to residential properties, but  for legionella regulations hot water at the tap should be 50 Celsius. 60 Celsius in a storage vessel.

 

[ProDave]

1 hour ago, joe90 said:

 

I forget who it was but someone slowly raised their DHW temp to the point where they could only just hold their hand under the tap and measured the temp at 47’. Raising the temp higher only just wastes energy (IMO).

That might have been me.

 

My DHW set point is 47 degrees at the moment. At that, I can just hold my hand under a running hot tap, so hot enought for what I recon is the hottest task, dishwashing, as long as you don't add any cold water to it.  I see no point it heating it any hotter with the HP.

 

At this temperature it is more than hot enough for showers or a bath, and still leave plenty of capacity for later on when solar PV is fitted for heating the water further by excess PV generation.

[ProDave]

50 minutes ago, Tyke2 said:

Not relevant to residential properties, but  for legionella regulations hot water at the tap should be 50 Celsius. 60 Celsius in a storage vessel.

 

I raised that issue recently in a thread of my own, and the conclusion was it was near impossible for legionella to be present in the cold water mains supply, and with an unvented hot water tank there was no way for it to enter other than in the supply water, so heating it hotter was pointless.

[ProDave]

Slightly off topic but some are still concerned at heat pumps and point to "faulty" design.

 

I saw one such on a job this morning.  I noted a house I have worked at previously had just had a new Air source heat pump fitted.  I also noted that the heating medium appeared to be conventional sized wall hung radiators which will need to run hot. 

 

This seems to be one such poorly designed system where I feel near certain the results are going to disappoint and this will be yet another person saying how bad heat pumps are.

[AliMcLeod]

42 minutes ago, ProDave said:

I also noted that the heating medium appeared to be conventional sized wall hung radiators which will need to run hot. 

 

At what temperature should conventionally sized radiators ideally be run?

 

Looking ahead to winter weather (probably not too far off in Scotland) I'm trying to figure out the right balance for my UFH downstairs/radiators upstairs setup (our upstairs is only really used when we have visitors). We have Gas combi ( Bosch Greenstar 42CDi Classic), providing space heating and DHW. No Thermal store/water storage solution. 

 

At present, I have the boiler set to around 55C with the UFH manifold blending valve at 40C. The room stats control the UFH and they have started coming on in the morning. I suspect i'm getting some short cycling but not sure how I can avoid that with my setup.

Edited September 11, 2018 by AliMcLeod

[AliG]

@AliMcLeod It really depends on the heating requirement of the room the radiator is in. The hotter the water, the more energy you are putting into the room. I was looking at our UFH the other day and some of the manifolds only run at 27C as we don't need that much heat.

 

Assuming your insulation is good, 40C might work for the radiators too, especially as upstairs will benefit from heat rising from down the stairs.

 

I have the same issue as you in Edinburgh where the heating kicks in early in the morning when it is colder. I have Heatmiser thermostats in every room. If the rooms are occupied they are set at 21C. The house is well insulated, at the moment the south facing rooms never get below 21C, they may in the winter, the west and north facing rooms tend to drop to around 19C during the night. The heating then kicks in in the morning. However, if I leave the heating off they might well get up to 21C later in the day due to solar gain, heat from cooking etc. Indeed I can tell which rooms are occupied or where people have left lights on as this is enough to affect the temperature when I look at the Heatmiser app.

 

So ideally the heating wouldn't come on in the mornings as the house will heat up on its own, but for comfort reasons the family want it to be 21C when they get up.

[Tyke2]

1 hour ago, ProDave said:

I raised that issue recently in a thread of my own, and the conclusion was it was near impossible for legionella to be present in the cold water mains supply, and with an unvented hot water tank there was no way for it to enter other than in the supply water, so heating it hotter was pointless.

Hmmm. Not really. the cold water supply will regularly have elements of legionella present.

From HSE guidance:-

What is legionella?

Legionella bacteria is commonly found in water. The bacteria multiply where temperatures are between 20-45°C and nutrients are available. The bacteria are dormant below 20°C and do not survive above 60°C.

[Ed Davies]

Tangentially, at what temperature are conventional radiators rated? I think I read that the power output is normally given for 50 °C above room temperature (e.g, room at 20 °C, water at 70 °C) but that seems awfully hot. But then the manufacturers would want to give the highest power which is plausible. Any references?

[ProDave]

Just now, Ed Davies said:

Tangentially, at what temperature are conventional radiators rated? I think I read that the power output is normally given for 50 °C above room temperature (e.g, room at 20 °C, water at 70 °C) but that seems awfully hot. But then the manufacturers would want to give the highest power which is plausible. Any references?

I have never seen the figures, but radiators that are too hot to touch (so >50 degrees) has always seemed normal to me in any house I have seen with radiator central heating.

[ProDave]

4 minutes ago, Tyke2 said:

Hmmm. Not really. the cold water supply will regularly have elements of legionella present.

From HSE guidance:-

What is legionella?

Legionella bacteria is commonly found in water. The bacteria multiply where temperatures are between 20-45°C and nutrients are available. The bacteria are dormant below 20°C and do not survive above 60°C.

An analysis from @JSHarris from my thread

But given that there has never been a case of pneumonia in the UK that has been traced to a domestic hot water system, that contracting pneumonia from Legionella Pneumophila is extremely rare, that the vast majority of cases of pneumonia in the UK are caused by streptococcus pneumoniae, with the rest being caused by other bacteria, viral, or even fungal, infections, then my personal view is that the risk of legionella within a domestic hot water system is already very, very low. 

 

The risk from a sealed, anaerobic, hot water system, fed with treated water from an ultrafiltration plant, which in turn is fed by a source that is, cold, slightly acidic and has a low oxygen concentration is so close to zero as to not be worth worrying about.

 

You are far more likely to catch pneumonia caused by Legionella Pneumophila from someone in your local supermarket checkout queue that's just come back from a  holiday in Spain...

 

Thread here

 

[Tyke2]

28 minutes ago, ProDave said:

An analysis from @JSHarris from my thread

 

 

 

Thread here

 

I probably agree. Perhaps it just illustrates that the law in connection to legionella is very belt and braces.

In my day job in NHS premises if I had a tap discharging water at 40 to 48 degrees there would be a proper panic on.

[Ferdinand]

3 hours ago, joe90 said:

I hope you are correct on the issue of the heat rising upstairs. I am aware that one of the companies I worked for did a UFH downstairs and radiators upstairs. I was not involved but am told the radiators with TRV's never actually came on, so you may be correct.

 

I have that, but it is run as 2 systems with 2 controllers fed from one boiler.

 

My house is OK rather than superinsulated ... 2010 regs then a bit.

 

Ferdinand

 

[A_L]

1 hour ago, Ed Davies said:

Tangentially, at what temperature are conventional radiators rated? I think I read that the power output is normally given for 50 °C above room temperature (e.g, room at 20 °C, water at 70 °C) but that seems awfully hot. But then the manufacturers would want to give the highest power which is plausible. Any references?

 

@Ed DaviesNo references, but 70°C is the usually quoted output temperature,  its about the highest flow temperature where the return can be expected to cause 'condensing' in the boiler. 

Relative to 70°C outputs at 30°C/13.5%,  40°C/32.1%,  50°C/53.0%,  60°C/75.8% for rooms at 20°C and 'ordinary' radiators

[ProDave]

1 hour ago, Tyke2 said:

I probably agree. Perhaps it just illustrates that the law in connection to legionella is very belt and braces.

In my day job in NHS premises if I had a tap discharging water at 40 to 48 degrees there would be a proper panic on.

There is talk (it may even have happened) of domestic rentals requiring a legionella risk assesment.

 

In your case it could very well be different, it might be open vented cold water storage tanks in relatively warm plant rooms feeding via a calorifier to the hot taps, where the risk may be very very different to my situation.