Major modifications to heating system

[JohnMo]

Basics.

190m2 single storey UFH throughout.  UFH pipes at 300mm centres.  House heat load max 3kW.

 

Atag A325ECX combi boiler min turndown 6kW.

 

160l buffer, utilising an unvented thermal store with indirect boiler coil and DHW coil.  Summertime use is for excess solar from PV to heat tank and use instead of boiler for DHW.

 

Issue 1, when used at low temperatures the heating coil is way to small, had to turn boiler up to around 50 deg flow temp to get the buffer to 34 deg.  

 

Issue 2, a cold slug of water would enter the boiler with the tank hot in summer and the boiler would fire up, until the hot water came through, using gas.

 

Issue 3 heat loss when heated by PV to 70 degs.

 

Issue 4, could only get down to 30 degs at the UFH mixer.

 

Fixes.

Issue 1, large 40 PHE installed, with pump as well as being connected to indirect coil.  Flow switch on boiler side, when it's pump starts the buffer side pump starts.  First test had a temp delta of of boiler flow and return of 7 degs with a 30 deg flow temp.  That kept boiler happy.  An approach temp difference of 2 degs on buffer side.  So boiler fired at 30 heating gets 28 deg.

 

Issue 2, installed solar diverter valve and mixer.  If flow from DHW coil is above 43 deg, water goes direct to taps, mixer valve ensures water is below 50 deg.  If water below 43, goes to combi for further heating.

 

Issue 3 loads of insulation., Had glass wool sound proofing 70mm thick laying about and vapour protection material laying about.  Made suitable sizes cushion to insulate tank and pipe insulation.

 

Issue 4 installed a bypass mixer and Salus self balancing actuator at the outlet of the buffer, this manages the delta T from UFH, so should give my lower temps at the mixer valve, which can now be a safety feature instead of actively controlling temp.  See last image, second image is just a linear actuator.

 

Photos show different states of mods.

 

 

[Iceverge]

I'm intrigued but also confused. 

 

Do you have any sketch/schematic of your setup to share? 

[JohnMo]

Quick rough sketch

[JohnMo]

So an update on the heating and hot water performance.

 

DHW

Prior to modes, May 2022 gas consumption, for domestic hot water was 260kWh, or 8kWh per day.

 

After mods

June - 105kWh or 3.5kWh a day

July - 64kWh or around 2kWh a day

August - 104kWh or 3.5kWh a day.  Had visitors (extra 4 in house) for a long weekend.  All other times we were home.

 

So overall well worth the mods.

 

Heating

Had the heating on the whole of October, set up to use weather compensation.  Flow temps through UFH start at 23 degrees, compensation curve is almost flat, max temp at -5 is 26 degs. Night set back is a 2 degree drop in flow temp.  However due to the inertia of the house/floor, night set back starts at 17:30 and finishes 02:30.

 

Floor temp is around 21degs.  Room temps 19 degs.  Bedrooms temp sits at about 18 degs.

 

All rooms have UFH circulation on, as the thermostats are set at 22, so operate as a single zone.

 

Min turndown of boiler at the flow temps is 6.7kW.  But my average gas input into the UFH water is  currently 0.5kWh per hour.  Boiler runs for about 10 mins and is off for nearly 2 hrs.  At -5 the boiler run time should run around 15 mins and off 20 mins.

 

One observation is the gas usage is well below what Jeremy spreadsheet say I should be consuming to keep the house at this temperature.

 

Based on last year's October gas input of 1370kWh for heating and DHW.  This year I hope to consume 600kWh or so.

 

So a reduction of about 50% overall.😁

 

[JohnMo]

Forgot to mention, took the Salus actuator off the mixer valve and it is basically closed so mixing, water just passes through.  Wasn't needed.

[joth]

3 hours ago, JohnMo said:

One observation is the gas usage is well below what Jeremy spreadsheet say I should be consuming to keep the house at this temperature.

Obv you'll be getting some heat from electrical devices, solar gains, cooking, humans trotting around the building etc which as a fixed source becomes more and more significant the more you reduce the overall demand. It'll be interesting to see if the % error vs spreadsheet reduces in the very coldest part of winter. 

 

 

Excellent work on the projects! The DHW reductions are startling 

Edited October 15, 2022 by joth

[Nickfromwales]

On 26/06/2022 at 14:24, Iceverge said:

I'm intrigued but also confused. 

As was I.

Knee-jerk was to dump the wasteful open vented combination store and just go to an UVC for collecting excess PV for summer DHW ( keeping the dual TMV DHW arrangement which I like a lot and will use at mine when the UVC goes in prior to my gas combi ).

BUT…….

Seeing that the combination store is also the buffer for space heating, and that the space heating demand will be waaaaaay lower than what’s needed at mine, I now get it.

Hats off, results speak for themselves  Tres Bien.

[JohnMo]

Thanks for the comments, but I have say Nick the idea for the system came from you, and some of your earlier posts on here.  I had to do a little refinement at the end but you always do with things that a bit different. The bit that took the most getting my head around was the heat transfer rates through a cylinder coil at very low temps is really poor.

 

When I first started heating the house I was very confused how I could be using so much gas.  Had never really come across short cycling, as all my previous House's had been heat seizes.

 

I suppose that's why I keep banging on about, heating system design and the need to design it, to eliminate short cycling - because you can use twice the input energy you should.

[Onoff]

13 minutes ago, JohnMo said:

Thanks for the comments, but I have say Nick the idea for the system came from you

 

He may look silly but...

[Nickfromwales]

3 hours ago, JohnMo said:

Thanks for the comments, but I have say Nick the idea for the system came from you, and some of your earlier posts on here.  I had to do a little refinement at the end but you always do with things that a bit different.

Actually kudos to @Jeremy Harris as I quite liked a lot of his ideas for his first setup, much as you have there, so I built on that as a ‘game changer’ in how I thought things through. He had the exact same combination cylinder as you’ve installed, but then ditched it due to the significant latent heat loss, using a SA instead.

 

I’m very much still learning / improving myself btw….   Such a great forum, just for the diversity of the members and their knowledge and comprehensive feedback, which is simply gold dust. 

[JohnMo]

Must agree, the site is excellent.

 

The cylinder as standard does leak lots of heat.  Loads of extra insulation has helped.  Today it's sitting at 25/26, so heat loss is minimal.  In the summer if it is hot it's from excess PV, it occasionally gets to 70 and the room used to be quite warm, the insulation made a dramatic difference to room temperature and also rate the cylinder heated up.

 

Sun's out today, no real need to have the heating on, but with weather comp, the pumps are still running, so excess PV is going to the immersion and is charging the floor.

[JohnMo]

Update

 

October final figure

So gas consumption compared to 2021

 

2021 - October used 1,370 kWh for DHW and UFH or (assuming 5kWh DHW) 1,220 kWh for UFH only

2022 - October used 562 kWh or 412 kWh for UFH only

 

Saving 59%

 

Interesting the Jeremy heating spreadsheet, for November predicts 884kWh for heating only.  So basically used half that, 2 people in house plus dog and solar gain all help.

 

November

Issues and changes made at the start of November

 

Weather Comp switched off

New UFH mixer, now have an IVAR mixer, with low temp thermostatic mixing valve.  Much better control than the previous Reliance one.

Heat meter installed upstream of UFH.

 

Had the heating off for a couple of days at the start of November.  When I restarted it the gas consumption started getting much higher than I was expecting.  Had a fiddle with WC curves, but this made no real difference. 

 

WC was dumped in favour of charging the buffer to set temperature based on a thermostat and running the UFH in batch charging mode. UFH starts at 1 am and continues running until the room thermostat (in hall) gets to 18.5 degs,  it then is switched of the UFH. Basically all UFH loops are open except bedrooms on a single zone, bedrooms are heated by opening the doors to the rest of the house.  Still fine tuning, but flow temp set to 30, buffer (thermal store) I have set to 50 degrees, this ensures the odd opening of tap doesn't fire up the combi as the water leaves the thermal store DHW coil hot enough to by passed around the combi.

 

November gas consumption compared to 2021

 

2021 - November used 1,754 kWh for DHW and UFH or (assuming 5kWh DHW) 1,604 kWh or UFH only

2022 - November used 1,138 kWh or 988 kWh for UFH only

 

Saving 35.1%

 

Interesting the Jeremy spreadsheet, for November predicts 1102kWh for heating only.  This is showing less of a percentage difference than October.  Explained by more heat being lost to the building fabric, possibly less solar gain, but still some.

 

Average temp below zero for next week, so will see how this goes.

[JohnMo]

Just to complete this thread off. Continued to get reduced gas consumption, until the heating went off in April, with the previous mods made and a slightly changed operating mode. The heat meter installed showing circa 108 to 110% boiler efficiency.

 

Weather compensation, proved to work well when it was cold (3-4 degs or below OAT), but less effective as it became warmer using more gas than expected.  So moved to a weather compensated UFH batch charge. Set a WC curve that required approx 7 hours to charge the floor and used a 0.1 hysteresis timer/thermostat to control when the heating started and stopped.  Approx. start time was midnight and end time 7am.  If there had been solar gain during the day the thermostat would be later starting the UFH, if the curve was out, the thermostat would catch it either allowing over or under run times, so switch the heating off sooner or later than 7am.

 

Things I found when setting up and monitoring

• Low flow temp and gas boiler gives a big jump in boiler efficiency - from low 90s running at 50 deg to over a 100% in the low 30s.
• UFH manifold mixers always mix return and incoming flow, so to flow 30 degs in the UFH loop you need to provide around 34 degs at the inlet of the mixer.  And to get that close required lots of balancing of the flow screws within the mixer.
• Gas boilers can be problematic in low energy houses, either requiring a huge buffer or a small boiler with lots of turn down.

Next

• Have now installed an ASHP (eBay bargain) used plenty of the lessons learned from experimentation, plus I wanted some summer cooling.
  • My original UFH setup had a boiler pump, buffer pump and UFH pump, with 2 of the pumps running 24/7 during heating season.  Using approx 260kWh of electric (£90 at todays cost).  This has been reduced to ASHP circulation pump only, which only runs when there is a demand for heat. Now only have one thermostat, that can do either heating or cooling. No actuators on the manifold. Have also connected UFH to summer house that will be used all year round.  
  • UFH has no mixer or pump, run direct from ASHP (both house and summer house). Used a mix of 28mm, 22mm and 15mm  Hep2O and copper to connect everything up. One issue was connecting the DHW cylinder, as I reused the original boiler to UFH pipes in 22mm.  The long pipe run gave a pressure drop issue. To resolve I added an additional pump used only for DHW heating in the return line from the cylinder. This pump only runs would the 3 way valve is energised for DHW heating, so runs less than an hour a day.  
  • Can now do UFH cooling.  Currently running floor cooling when house is above 20.5 degs, basically running off PV, generally runs 8am to 5pm, with a while off when DHW occurs at 9am. Flow temp set to 12 degs though UFH loops, no buffer on a single zone, 6kW ASHP has been set to run minimum Hz, almost whisper quiet and runs for approx 20 mins at a time, so only 2 to 3 cycles per hour. EER (CoP for cooling) is around 5.5 to 7, so pulls about 1kW or less from the solar PV available.
  • Heating will have to wait to Oct to see what I need to setup, preliminary WC curve setup..

[Lofty718]

How do you find the cooling with the UFH pipes? is it effective? It's something I'm considering in the future

 

All the engineers I know would say 300mm pipe centres and an ASHP are a no no, 150mm max

[JohnMo]

1 hour ago, Lofty718 said:

All the engineers I know would say 300mm pipe centres and an ASHP are a no no, 150mm max

They obviously know no different or better, possibly only worked on houses with poor insulation. Prior to the ASHP with the gas boiler and mixer we had 30 deg flow at below zero outside. Worked fine.

 

The heat pump seems happy enough and is certainly pulling heat from the floor, as runs for about 20 mins at a time. If it had nothing to transfer it's cool water to it would just short cycle.

 

300mm works fine for cooling (it's not Aircon cold), and maybe not as good as 150mm could be, but takes some the extreme heat out of the house. It has a cool feel when you go in, but the air temp may not be as cool as you would think. I think the floor pulls the heat from you, opposite to UFH heating.

 

I realised this morning the cooling didn't come yesterday or this morning at all, due to communication issues with DHW, so the ASHP never switched off DHW.  The house was noticeably hotter last night. That hiccup is now fixed.

 

 

Edited June 15, 2023 by JohnMo
Missed details

[Lofty718]

My centres are 200mm and they were telling me they were too big. But I can run the floor at 30c flow temp on a 10c day and it's comfy (gas boiler) with weather comp

 

Is there anything different needed to install UFH suitable for cooling? Could i just install an ashp and reverse it as easy as that?

Edited June 15, 2023 by Lofty718

[JohnMo]

Nothing extra needed except you need a thermostat that can do cooling and heating. I am using a Computherm Q7RF. I operate the whole UFH as a single zone. You need to call for heat the opposite way, when looking at cooling v heating.

 

My ASHP has a summer winter switch, in summer it does DHW and cooling, in winter DHW and heating. Not all ASHP do cooling out the box, so check the ones offered do.

 

It's hotter today than yesterday and the house definitely feels cooler today with the cooling on, than yesterday when it was off.