Bloody ridiculous

[Iceverge]

4 hours ago, JamesPa said:

buffer tanks

 

Why are these an issue?  I would have thought they would reduce cycling in times of low demand? 

 

(A2A in our house not A2W so a bit ignorant of some of it). 

 

 

[JamesPa]

2 hours ago, Iceverge said:

Why are these an issue?  I would have thought they would reduce cycling in times of low demand? 

To be clear I'm referring to a 4 port buffer tank, or indeed a 4 port llh or phe in a domestic situation other than a mansion.

 

In principle they aren't an issue.  In practice they are almost invariably, it seems, badly specified and/or badly controlled and so cause mixing between flow and return.  This means you have to increase the flow temperature for any given emitter temperature, reducing COP significantly.  In extreme cases the mismatch in pump speeds either side can deprive the heating system of energy and compromise defrost.  They are mostly installed principally to protect installers from call outs, not for any legitimate system reason.  Finally they make fault diagnosis more difficult and mask issues that should be corrected.  Unfortunately many installers still use them but interestingly will not defend their position when asked to on the Renewableheating hub podcasts about buffers.

 

A 2 port buffer tank, also called a volumiser, will still reduce cycling and suffers from none of the above problems.

Edited April 24 by JamesPa

[JamesPa]

5 hours ago, JamesP said:

Can you be a bit clearer if anything added / improved to the fabric of your home, glass, wall and loft insulation.

Even with subsidies what is the financial cost?

 

Not when I put the ashp in. 

 

It's a 1930s house with two modest 1980s extensions.  About 80pc of the otherwise solid walls have iwi.  The upvc double glazed windows are from the 1980s, glass replaced with low e argon filled, frames original.  There are in addition three crittal metal framed windows with perspex sheets to give a bit of secondary glazing.  There is no underfloor insulation anywhere, but the loft has 30cm. The insulation upgrades have been done piecemeal over 20 years as rooms have been redecorated.

 

The ashp install cost 6k after grant replacing an aging boiler which was nearing end of life. The dhw system, previously indirect with very noisy pumps, is revolutionised and the heating much more comfortable.  Running cost 20pc less for greater comfort. It is definitely an upgrade. Does that answer your question?  

[JohnMo]

10 minutes ago, JamesPa said:

2 port buffer tank, also called a volumiser

They are not the same thing, a 2 port buffer would straddle flow and return and provide hydraulic separation, a volumiser will sit in either the supply or return pipes (not both) and provide zero hydraulic separation.

 

Buffers are in general bad because they introduce distortion, which in basic terms is a difference in flow temp on the primary and secondary sides of the system. The ASHP will therefore run hotter than is actually needed. If flow rates are equal each side in the primary and secondary circuit then distortion doesn't occur, but if that's the case the buffer is serving no purpose, so the additional pump is an additional electric drain.

[JamesPa]

4 minutes ago, JohnMo said:

19 minutes ago, JamesPa said:

2 port buffer tank, also called a volumiser

They are not the same thing, a 2 port buffer would straddle flow and return and provide hydraulic separation, a volumiser will sit in either the supply or return pipes (not both) and provide zero hydraulic separation.

Thanks for that clarification Many installers still seem to call 2 port devices in one of the supply pipes a buffer tank, but I'm happy to hear that this is incorrect terminology.  I shall from now on say '2 port volumiser, sometimes incorrectly called a buffer!'

Edited April 24 by JamesPa

[JohnMo]

A 2 port buffer looks like this - the grey box being the heat pump 

 

[JamesPa]

13 minutes ago, JohnMo said:

A 2 port buffer looks like this - the grey box being the heat pump 

 

Presumably just as bad as 4 port?

[JamesPa]

2 hours ago, Beelbeebub said:

7 hours ago, JamesPa said:

With the new Mitsubishi 2 compressor (2+6kW) heat pump

Can you expand on this? I know they have some massive commercial systems that have 2 compressors but I was unaware of any small domestic units.

The 8kW (NB not 8.5kW) r290 model has a 6kW inverter driven compressor and a 2kW fixed compressor.  SOFAIK it's a first in the domestic market.

[JamesPa]

@Iceverge

 

Your 40kW boiler will not deliver anything like 40kW because few houses have that much emitter capacity, which in practice is the limit in most cases.

 

Unless you only heat the air and not the fabric (which is possible with an A2A heat pump used for short periods of time) or your house is very lossy, your house will continue to lose heat even if the heating is switched off, at a rate not much slower than if it is switched on.  That heat still has to be replaced, so your part time heating doesn't actually save anything like as much heat as people suppose in the vast majority of use cases.  I would therefore dispute your contention that ashps are unsuitable for houses only occupied part time but accept you may have to get a bit more efficiency to match running costs.  That said with a couple of fancoils strategically placed you can likely get the best of both worlds.

Edited April 24 by JamesPa

[SteamyTea]

3 hours ago, Beelbeebub said:

other option would be to make 1 unit, say max 7kw. But make it really easy to just stick 2 units side by side

I made a similar suggestion some years ago.

The compressor is not the expensive part of the unit.

 

One problem with 'adding an extra unit' is our planning law. I think there is a 0.6m³ rule, over that requires planning, no matter which fits it.

Like the electricity market, our planning rules need a major overhaul.

[JamesPa]

3 minutes ago, SteamyTea said:

I made a similar suggestion some years ago.

The compressor is not the expensive part of the unit.

 

One problem with 'adding an extra unit' is our planning law. I think there is a 0.6m³ rule, over that requires planning, no matter which fits it.

Like the electricity market, our planning rules need a major overhaul.

The rules are, I believe, shortly to be changed to allow a second pump.

[SteamyTea]

53 minutes ago, JamesPa said:

The rules are, I believe, shortly to be changed to allow a second pump.

Good.

 

I often say 'for every rule we have that says you must do something, we have another rule that says you can't'.

 

[Iceverge]

1 hour ago, JamesPa said:

@Iceverge

 

Your 40kW boiler will not deliver anything like 40kW because few houses have that much emitter capacity, which in practice is the limit in most cases.

 

Unless you only heat the air and not the fabric (which is possible with an A2A heat pump used for short periods of time) or your house is very lossy, your house will continue to lose heat even if the heating is switched off, at a rate not much slower than if it is switched on.  That heat still has to be replaced, so your part time heating doesn't actually save anything like as much heat as people suppose in the vast majority of use cases.  I would therefore dispute your contention that ashps are unsuitable for houses only occupied part time but accept you may have to get a bit more efficiency to match running costs.  That said with a couple of fancoils strategically placed you can likely get the best of both worlds.

 

Is your house kept at the same temperature constantly or do you intermittently heat it?

 

 

 

[JohnMo]

3 hours ago, JamesPa said:

Presumably just as bad as 4 port?

Not necessarily. A 4 port all flow and all returned water flows through the buffer. A 2 port, only when the flow on primary side is higher than secondary (a zone is closed for example) does any water go through buffer. The control of a 2 port are also different.

 

A 2 port control is:

Heat source is there to only satisfy a thermostat on the buffer. The heat source stops and starts only against that thermostat. The secondary side is run from the house thermostat(s). 

 

After playing with most versions of buffer and a volumiser, my heating runs far better without a buffer or volumiser, and definitely better without zones.

[JohnMo]

1 hour ago, Iceverge said:

Is your house kept at the same temperature constantly or do you intermittently heat it?

We heat intermittently, but house stays pretty stable temperature wise.

 

So today our average temp over the day is about 8 degs, so we are still in heating mode, but are getting plenty of solar. So heating is generally powered by PV (since start of March) and a floating battery state of charge to get reasonable run times. So the heating is free - can't do that with gas or oil or with direct electric heating (without a solar farm).

 

So turns a modest PV excess of 7.6kWh in 32kWh. Any additional went into hot water via immersion

[JamesPa]

17 hours ago, Iceverge said:

Is your house kept at the same temperature constantly or do you intermittently heat it?

 

At the current time, like @JohnMo, its heated intermittently, because the ASHP cant possibly modulate down far enough and  there is anyway solar gain during the day, so the heating switches itself off from about 9am till 10pm.  The house stays at a fairly constant temperature because of thermal mass/solar gain.  Unlike @johnmo I don't have a big concrete slab, its a 1930s house remember, but the heat capacity is nevertheless roughly 20kWh/K.  The loss at -2C is about 7kW, so even at -2 it takes 3 hrs to drop a degree, at a more average 7C its nearer 6hrs to drop a degree, hence little saving in loss (and thus heating bills) from part-time heating

 

Over the past 5 years I have gone successively from

• gas fired, intermittent heating throughout the season, trvs everywhere, flow temperature as installer left it (ie high, about 75C) 
• gas fired, heating 24*7 in the height of the season, intermittently towards the ends of the season, trvs everywhere; flow temperature turned down to 50 (lowest possible on my boiler most of the season), 55 in the height of the season (necessary to get enough out of the rads)
• ASHP, set to heat 24*7, in practice heating 24*7 in the height and shoulder of the season, intermittently towards the ends of the season.  Only 2 rads out of 16 with any form of thermostatic control otherwise open loop

 

Each step has both increased comfort (because of reduced thermal gradients) and reduced my bills.   I'm now looking at bills 25% lower than when I was doing the 'conventional' thing of gas boiler with bells and whistles controls and heating early morning and afternoon/evening only.  The comparison is like for like, ie I have taken out the effect of price changes, and is actually an underestimate because I am not taking into account the fact that some of my space heating now comes from solar (unlike @JohnMo this isn't free because I get paid 15p/kWh for export, but it is less than my import rate)

 

I would be dismissing this as chance were it not for the fact that there are good thermodynamic arguments why excessive zoning (whether in time or space) reduces the house energy demand by much less than the manufacturers of complex controls like us to believe.   See Heatgeeks discussions on this from time to time.

 

Of course the detail will vary from house to house.

 

 

 

Edited April 25 by JamesPa

[JohnMo]

24 hours later, we are now in cooling mode. Cooling switched on this morning.

 

That will be left to get on with it until end of September now. Running pretty much a fixed temp. So far today running 15 mins on/25 mins off cycle this morning getting a negative CoP of just over 8. Yes 8 - you have to love a heat pump.

[JamesPa]

1 minute ago, JohnMo said:

24 hours later, we are now in cooling mode

 

2 minutes ago, JohnMo said:

you have to love a heat pump.

 

There used to be such things as gas fridges for use on boats (maybe there still are), so I suppose one could make a gas powered cooling system. 

 

Given the US obsession with both aircon and fossil fuels, I'm surprised that it hasn't yet been mandated by executive order.

[Nickfromwales]

56 minutes ago, JamesPa said:

I'm surprised that it hasn't yet been mandated by executive order.

Don't give him any more ideas......🙄

[Iceverge]

3 hours ago, JamesPa said:

At the current time, like @JohnMo, its heated intermittently, because the ASHP cant possibly modulate down far enough and  there is anyway solar gain during the day, so the heating switches itself off from about 9am till 10pm.  The house stays at a fairly constant temperature because of thermal mass/solar gain.  Unlike @johnmo I don't have a big concrete slab, its a 1930s house remember, but the heat capacity is nevertheless roughly 20kWh/K.  The loss at -2C is about 7kW, so even at -2 it takes 3 hrs to drop a degree, at a more average 7C its nearer 6hrs to drop a degree, hence little saving in loss (and thus heating bills) from part-time heating

 

Over the past 5 years I have gone successively from

• gas fired, intermittent heating throughout the season, trvs everywhere, flow temperature as installer left it (ie high, about 75C) 
• gas fired, heating 24*7 in the height of the season, intermittently towards the ends of the season, trvs everywhere; flow temperature turned down to 50 (lowest possible on my boiler most of the season), 55 in the height of the season (necessary to get enough out of the rads)
• ASHP, set to heat 24*7, in practice heating 24*7 in the height and shoulder of the season, intermittently towards the ends of the season.  Only 2 rads out of 16 with any form of thermostatic control otherwise open loop

 

Each step has both increased comfort (because of reduced thermal gradients) and reduced my bills.   I'm now looking at bills 25% lower than when I was doing the 'conventional' thing of gas boiler with bells and whistles controls and heating early morning and afternoon/evening only.  The comparison is like for like, ie I have taken out the effect of price changes, and is actually an underestimate because I am not taking into account the fact that some of my space heating now comes from solar (unlike @JohnMo this isn't free because I get paid 15p/kWh for export, but it is less than my import rate)

 

I would be dismissing this as chance were it not for the fact that there are good thermodynamic arguments why excessive zoning (whether in time or space) reduces the house energy demand by much less than the manufacturers of complex controls like us to believe.   See Heatgeeks discussions on this from time to time.

 

Of course the detail will vary from house to house.

 

 

 

 

All understood, 

 

Perhaps I'll rephrase my question. 

 

Do you keep your house at the same temperature 24/7 ?

 

 

When we rented a cottage we never used the heating unless we were in situ as it lost heat very quickly, almost to the point of being as cold as outside. 

 

The heating came on perhaps from 7-8am and then from 6pm until bedtime when we got home from work and maybe once or twice in the night time. Of course it's wasn't the most comfortable but it was the most economical use of oil for us. 

 

 

[marshian]

3 hours ago, JamesPa said:

At the current time, like @JohnMo, its heated intermittently, because the ASHP cant possibly modulate down far enough and  there is anyway solar gain during the day, so the heating switches itself off from about 9am till 10pm.  The house stays at a fairly constant temperature because of thermal mass/solar gain.  Unlike @johnmo I don't have a big concrete slab, its a 1930s house remember, but the heat capacity is nevertheless roughly 20kWh/K.  The loss at -2C is about 7kW, so even at -2 it takes 3 hrs to drop a degree, at a more average 7C its nearer 6hrs to drop a degree, hence little saving in loss (and thus heating bills) from part-time heating

 

Over the past 5 years I have gone successively from

• gas fired, intermittent heating throughout the season, trvs everywhere, flow temperature as installer left it (ie high, about 75C) 
• gas fired, heating 24*7 in the height of the season, intermittently towards the ends of the season, trvs everywhere; flow temperature turned down to 50 (lowest possible on my boiler most of the season), 55 in the height of the season (necessary to get enough out of the rads)
• ASHP, set to heat 24*7, in practice heating 24*7 in the height and shoulder of the season, intermittently towards the ends of the season.  Only 2 rads out of 16 with any form of thermostatic control otherwise open loop

 

Each step has both increased comfort (because of reduced thermal gradients) and reduced my bills.   I'm now looking at bills 25% lower than when I was doing the 'conventional' thing of gas boiler with bells and whistles controls and heating early morning and afternoon/evening only.  The comparison is like for like, ie I have taken out the effect of price changes, and is actually an underestimate because I am not taking into account the fact that some of my space heating now comes from solar (unlike @JohnMo this isn't free because I get paid 15p/kWh for export, but it is less than my import rate)

 

I would be dismissing this as chance were it not for the fact that there are good thermodynamic arguments why excessive zoning (whether in time or space) reduces the house energy demand by much less than the manufacturers of complex controls like us to believe.   See Heatgeeks discussions on this from time to time.

 

Of course the detail will vary from house to house.

 

Really interesting info - I've gone thro similar albeit still using gas boiler

 

Over the past 4 years I have gone successively from

• gas fired, heating to a schedule trvs everywhere, flow temperature pinned at 68C and rooms all set to different target temps "probably over zoned"

• gas fired, heating to a schedule trvs everywhere, upgraded rads lower flow temps 48C was pretty much as low as the boiler would go to 55C in the worst of winter (best description is manual WC) - I was using "hour boosts" in shoulder seasons when house needed a little heat but a full schedule was too much.

• heating 24*7 still got trvs everywhere but majority set too a temp that cannot be achieved WC flow temp (32C at 0C OAT) (I still have a couple of areas where effectively the TRV's are in operation but they are high heat loss areas)

In the last few weeks I've been experimenting with turning of the boiler for a several hours during the day and I'm rapidly coming to the conclusion that it's not saving me any energy - or rather energy not being used during switched off period is being used to get the house back up to temp

 

Comparing energy used v HDD data it's pretty clear to me that proper WC (using OAT sensor and the correct curve) combined with open zones is a way more comfortable environment at the expense of a slight increase in energy usage * over the winter period (* compared to Scheduled heating)

 

That increase in energy usage is now being recovered as a result of WC being far more efficient at keeping the majority of the house at target temps now we are in the shoulder seasons so where I was considering going back to scheduled heating or turning off the heating for periods I'm leaving it 24/7

 

Data

 

HDD
Month	2022	2023	2024	2025
Jan		377	366	414
Feb		294	248	332
Mar		291	251	288
Apr		239	211	161
May		141	101
Jun		55	84
Jul		39	45
Aug		42	31
Sep	28	38	88
Oct	116	130	159
Nov	217	283	278
Dec	399	291	300
Total	759	2,219	2,161	1,195

 

KW (Heating only)
Month	2022	2023	2024	2025
Jan		1,388	1,440	1,901
Feb		1,076	942	1,507
Mar		1,056	814	1,024
Apr		604	600	342
May		99	38
Jun		24	54
Jul		-	41
Aug		5	-
Sep	108	8	183
Oct	384	399	651
Nov	776	663	868
Dec	1,442	1,146	1,429
Total	2,710	6,468	7,061	4,774

 

 

KW/HDD
Month	2022	2023	2024	2025
Jan		3.68	3.94	4.59
Feb		3.66	3.80	4.54
Mar		3.63	3.25	3.55
Apr		2.52	2.84	2.12
May		0.70	0.38
Jun		0.44	0.64
Jul		0.00	0.91
Aug		0.12	0.00
Sep	3.88	0.22	2.07
Oct	3.32	3.08	4.11
Nov	3.57	2.34	3.12
Dec	3.62	3.94	4.77
Avg	3.57	2.91	3.27	3.99

[SteamyTea]

1 hour ago, marshian said:

KW

kW

[JamesPa]

1 hour ago, Iceverge said:

When we rented a cottage we never used the heating unless we were in situ as it lost heat very quickly, almost to the point of being as cold as outside. 

 

Heating a building that has the same thermal characteristics as a tent does definitely require a different approach, for example an open fire so most of the effect is both instantaneous and radiant.  Fortunately they represent a relatively small proportion of our housing stock!

Edited April 25 by JamesPa

[SteamyTea]

4 minutes ago, JamesPa said:

^{a different approach, for example an open fire so most of the effect is both instantaneous and radiant.}

Or, most of the energy gets drawn up the chimney.

 

The formula for radiant energy is:

5.67x10^-8 W.m^-2.K^-4

So the 'window' that the radiant energy comes out of (the door usually) needs to be pretty large.

[JamesPa]

1 hour ago, SteamyTea said:

Or, most of the energy gets drawn up the chimney.

 

The formula for radiant energy is:

5.67x10^-8 W.m^-2.K^-4

So the 'window' that the radiant energy comes out of (the door usually) needs to be pretty large.

SOFAIK there is no good way to heat any building that has the thermal characteristics of a tent.   There are only various flavours of bad ways!  Like patio heaters, you are basically on to a loser!

Edited April 25 by JamesPa