@jamespa, @heatgeek Talk about laying the gauntlet down. In my view, you are both right depending on the task at hand, the variables and the required outcome.
Looking at the delivery side, to maintain a fixed output on the radiator, reducing the supply Delta T will require a reduction in flow temperature which will improve COP.
However, looking at the supply side, you can (from what I have been told) you can only reduce the Delta T to about 3.5 before it starts to affect performance. Covers to this, up to 10 Deg, will not significantly reduce performance. Daiken's fixed radiator Delta T is 10, this cannot be adjusted (you can adjust their fan coil and under floor settings). I cannot confirm if this is true, but I have just finished reassembling my improved test rig and have Mitsubishi and Panasonic units to run tests on just like I did for heating system design. On my test rig I can simulate radiator sizes, thermal mass, loading, internal and external temperatures. It was designed in conjunction with the Build Environment at Ulster University.
I do not like to believe what I am told, there are too many with vested interests that mould the truth to suit their own agenda. I try to test everything. The first things to test are 2 Delta T controllers I have developed, one for the Vaillent unit which just restricts flow and the second that controls a high output pump (160 KPA pressure) to suit units without a pump. This unit will also prevent freezing of the unit by pumping a very small amount of water, continuously.
Director at Heacol | Expert Heat Pump Consultant | Book a one-to-one consultation for pre- and post-installation advice, troubleshooting and system optimisation.
Hi All! I finally received my updated quote from Sustain. Looking at efficiency it seems on par with smartheating (reattach it here too). Based on that alone, Sustain offers a better price. However, I guess that's not the only consideration at stake...
There also still the Buffer issue that @JamesPa highlighted I suspect.
In addition, when I invested on solar panels I thought that I had to stay at least 5 years in this property. Now adding this work on top makes me wonder if I have to add another 5 years on top in order to improve the overall financial impact of these choices. I did not give much ponder to it beforehand. Was I too naive?
Looking at the delivery side, to maintain a fixed output on the radiator, reducing the supply Delta T will require a reduction in flow temperature which will improve COP.
Sorry, but you have lost me here. Reducing DT requires a reduction in flow, not temperature surely. Assuming a fixed flow temperature, increase in DT will lower the average temperature of the radiator, thereby marginally reducing heat output, not maintaining fixed output, or am I smoking dagga (I wish).😊
Private individual. No affiliation with commercial "Heat Geeks" of same coincidental name.
@heacol Sorry, screwed this up. Misread your response. Reducing DT will require an INCREASE in flow, not temperature. A fixed flow temperature will increase the average temperature of the radiator, thereby marginally increasing heat output.
Private individual. No affiliation with commercial "Heat Geeks" of same coincidental name.
@jamespa, @heatgeek Talk about laying the gauntlet down. In my view, you are both right depending on the task at hand, the variables and the required outcome.
I hope I didnt offend, its just that' like you....
unless there is an explanation which is at least plausible. Alternatively I might believe observations (if I trust the observer) but not conclusions drawn ... unless there is a plausible explanation.
I like your distinction between 'supply' and 'delivery', it helps clarify!
However, looking at the supply side, you can (from what I have been told) you can only reduce the Delta T to about 3.5 before it starts to affect performance.
this is the argument I am puzzled by. It feels intuitively plausible, but I haven't heard an explanation nor is there an obvious one in the enthalpy/pressure diagram I referenced earlier. I can see that once delta T gets too small it might be difficult to measure and perhaps, given the error bars on cheap temperature sensors, this is an explanation. However in practice the heat pump could (possibly? presumably?) just control to flow temperature and so isnt trying to determine a difference, and if this is a degree or so off nominal it doesn't matter. Or does it need to measure the difference in order to stabilise the control loop for compressor modulation = power output - this is plausible at least!?
I would love to get to the bottom of this. The folks on openenergymonitor appear to assume that setting the optimum deltaT (ignoring practical issues like water velocity) is a straight trade off between water pump power consumptio0n and compressor power consumption.
@heacol OK, so you are arguing that TO MAINTAIN AVERAGE TEMPERATURE of the radiator, the flow temperature can be reduced with reduced DT. That figures, but how does this help the argument for increased DT?
Private individual. No affiliation with commercial "Heat Geeks" of same coincidental name.
Hi All! I finally received my updated quote from Sustain. Looking at efficiency it seems on par with smartheating (reattach it here too). Based on that alone, Sustain offers a better price. However, I guess that's not the only consideration at stake...
There also still the Buffer issue that @JamesPa highlighted I suspect.
In addition, when I invested on solar panels I thought that I had to stay at least 5 years in this property. Now adding this work on top makes me wonder if I have to add another 5 years on top in order to improve the overall financial impact of these choices. I did not give much ponder to it beforehand. Was I too naive?
~5K to you is a reasonable final price by the standards of pricing for ASHPs
The 3.5kW Vaillant is the 5kW Vaillant software limited so, unless the (probably small) price differential or the reduction in max noise due to the software limiting matters, you might has well have the 5kW one. The minimum outputs of the two are the same.
They list a buffer tank/volumiser (unpriced). I would very strongly advise to question which it is. A volumiser has 2 ports, buffer tank 4 ports and requires an additional water pump. As I have said already, you dont want a buffer tank.
I can't tell if they have included the internet interface, it might be worth asking (it can be retrofitted). 'Wireless room thermostat' is presumably only the sensocomfort (check!), the internet interface is separate. You dont need it unless you want one of
remote control
to be able to do some crude monitoring on your phone, which can be done on the sensocomfort but is less user friendly
to be able to do more sophisticated monitoring via Home Assistant (more sophisticated monitoring still via openenergymonitor has its own wifi interface)
to access the OVO heat pump add on tarrif
I haven't compared the rad swaps side by side between the front runners, it would be worth your while to do this as ultimately efficiency will depend on the rads assuming no buffer tank.
The solar panels will make a contribution to your heating during the shoulder season (I have been surprised how much in recent days), so will actually improve the payback time for these. The heat pump is of course a separate investment. I cant remember what your current heating is and how old which obviously is a factor. However the carbon reduction comes anyway and you should be more comfortable because of more stable interior temperatures.
Basically, if you are happy, I think you are there or thereabouts, subject to some final checks.
4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.
@jamespa thanks. I will take some time to make a head-to-head comparison btw these two quotes, and ask some final questions. If I decide for Sustain it may then be problematic to have the money I gave upfront for the Survey from HeatGeek but it would clearly be absorbed by the lower price with Sustain.
@eliuccio there are some very high level arguments in this thread which will be challenging at first read. Since you want to make a decision perhaps to ask the forum for further help you could try to make a summary of the arguments for and against each option and post them later and ask if you’ve got the gist of it?
2kW + Growatt & 4kW +Sunnyboy PV on south-facing roof Solar thermal. 9.5kWh Givenergy battery with AC3. MVHR. Vaillant 7kW ASHP (very pleased with it) open system operating on WC
@jamespa Hi I wrote to Sustain and I may wrote to Smart Heating as well for a couple of questions on radiators (1 more to replace?) and decommissioning of the boiler.
I have just started looking into both and run a comparative assessment using AI. I don't particularly feel it is a crucial element for me to decide but still useful as a map for more investigation:
### **Revised Comparative Analysis: Sustain vs. Smart Heating Proposals** Incorporating clarified details from Smart Heating’s updated proposal:
**Key Takeaway:** Sustain’s final price is **£2,699 cheaper**, even with identical grants.
---
#### **2. System Specifications** | **Component** | **Sustain** | **Smart Heating** | |--------------------------|--------------------------------------|---------------------------------------| | **Heat Pump** | Vaillant aroTHERM Plus 3.5kW | Vaillant aroTHERM Plus **5kW** | | SCOP at 45°C | 3.65 (365% efficiency) | **360% efficiency (SCOP 3.6)** | | **Cylinder** | 150L Unistor | 150L Vaillant uniSTOR | | **Radiator Replacements**| **4 radiators** (tailored to rooms) | **3 new radiators** + retained existing | | **Buffer Tank** | Included | Not mentioned | | **Warranty** | 5 years (heat pump) | **7 years (heat pump)** | | **Noise Compliance** | 42 dB at neighbors | **40.2 dB** (under permitted limits) |
**Key Takeaway:** - **Smart Heating** offers a larger 5kW heat pump and longer warranty but risks **oversizing** (home’s heat loss: 3.27kW). - **Sustain’s 3.5kW unit is better matched** to the home’s needs, reducing cycling and improving efficiency.
---
#### **3. Radiator Performance** - **Sustain:** - Replaces **4 radiators** with room-specific outputs (e.g., Kitchen: 123%, Bedrooms: 113–125%). - Bathroom radiator meets **45% demand** but notes reliance on adjacent heating.
- **Smart Heating:** - Installs **3 new radiators** (Kitchen: Type 22, Bed 2: Type 21, Living Room: Type 22). - Retains existing radiators in Bed 1 and Bathroom. **No heat demand % provided**, but outputs are: - Kitchen: 2,060W - Living Room: 1,720W (new) + 1,030W (existing) - Bed 2: 1,060W
**Critical Issue:** - Smart Heating’s retained radiators (e.g., Bed 1: 1,030W@dT50) may struggle at low flow temps. - Sustain’s design is **more transparent and tailored**, while Smart Heating’s reliance on existing radiators risks underperformance.
**Key Takeaway:** - Smart Heating’s flat £264/year savings are simpler but **less nuanced** than Sustain’s range. - Both systems use weather compensation, but Sustain’s buffer tank improves stability.
---
#### **5. Inclusions & Exclusions** | **Aspect** | **Sustain** | **Smart Heating** | |--------------------------|--------------------------------------|---------------------------------------| | **Buffer Tank** | Included | Not mentioned | | **Decommissioning** | Full removal of old system | Only "isolation" of existing system | | **Sound Assessment** | Detailed report | Compliant (40.2 dB) | | **Solar PV Integration** | Requires iBoost controller | Solar PV-ready (no controller cost) |
**Key Takeaway:** - Sustain includes **critical components** (buffer tank, decommissioning). - Smart Heating’s noise compliance is a regulatory advantage.
---
### **Final Recommendation** **1. Cost-Effectiveness:** - **Sustain wins** with a **£5,139 final price** vs. Smart Heating’s **£7,838**.
**2. System Design:** - **Sustain’s 3.5kW heat pump is better sized**, reducing cycling risks. - **Smart Heating’s 5kW unit risks inefficiency** but offers a longer warranty (7 years).
**3. Radiators:** - **Sustain’s radiator plan is more robust** (4 replacements, room-specific coverage). - **Smart Heating’s retained radiators** may underperform at low temps.
**4. Market Alignment:** - Sustain aligns with **best practices** (buffer tank, MCS compliance). - Smart Heating’s noise compliance and solar readiness are strengths.
---
### **Conclusion** **Choose Sustain** if: - You prioritize **lower upfront costs** and a **tailored radiator design**. - Oversizing concerns and cycling efficiency are critical.
**Consider Smart Heating** if: - A **longer warranty** and **quieter operation** are priorities. - You’re comfortable with potential radiator adjustments post-installation.
**Action Steps:** - Verify if Smart Heating’s retained radiators are compatible with low-flow temps. - Negotiate a buffer tank inclusion with Smart Heating to match Sustain’s stability.
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