This is my first post here. I'm looking into getting a heat pump installed in my three bedroom detached house. I've had two quotes so far and another heat survey booked in for a third quote.
I currently have a 12 year old gas condensing boiler in the garage. For the current pipe system, there are 22mm flow and return pipes which run from the garage to under the floor boards upstairs. The 22mm then tees off into 15mm pipe which runs in two directions: to the front of the house which supplies 4 radiators, and to the rear of the house which supplies 6 radiators. The radiators are connected by 10mm microbore. I don't think I have manifolds, so I'm assuming the the 15mm just tees off to each of the 10mm microbore in turn. This is all the information I have on the pipework.
According to the two heat surveys I've had done, they both estimate below 6kw heat loss (roughly 5.5kW - 5.7kW). I know from using the Heat Geek Cheat Sheet that the 10mm microbore is good for 1.15kW at 5deg DT and none of the rooms have a heat loss that exceeds 1 kW. So far so good. However, the 15mm is only good for 2.75kW and the run of 15mm pipe that supplies the 6 radiators has a total heat demand of 3.525 kW, which exceeds the 2.75 kW limit of the 15mm pipe at 5deg DT.
The installer for the first quote wants to replace all the pipework with 28/22/15mm dia and run a design flow temperature of 45deg with radiator upgrades.
The installer for the second quote (you can probably guess who) will leave the existing pipework as is and run a design flow temperature of 50deg with not-so-large radiator upgrades.
Neither installers have told me what my existing pipework is capable of, even after I've described the pipework to them. I know both installers will utilise weather compensation so the flow temperatures will be variable.
I feel that the pipe work over-hall associated with the first quote is unnecessary and costly. The cheat sheet shows 15mm capable of 3.85kW at 7deg DT, which is enough for the 6 radiators. On the other hand, a 50deg flow temp isn't optimal either as it will lose efficiency and reduce the life of the heat pump.
I feel both installers are imposing a one-size-fits-all approach and ignoring what is actually under the floorboards. I was hoping for someone to make an assessment of the existing pipework, or at least have it shown on paper how a 45deg flow temp won't work.
My preference is for a 45deg flow temperature as it allows for reasonably sized radiators and is in my opinion the most practically efficient solution for my home. I would like some advice on this. How can I get an assessment of my existing pipework? This would be extremely useful to know.
How can I get an assessment of my existing pipework? This would be extremely useful to know.
The problem is you need to know what the existing pipework is, which by the sounds of it you cant without taking up some floorboards. Then the question becomes, how to know what floorboards to take up because you presumably dont know where the pipes run.. You (or a plumber) could probably trace the pipework with a OR thermometer, see where they converge (cats are also good at finding hot spots, but Im not seriously suggesting that).
That said if you are fairly confident that the pipework does what you say, then 15mm is good for 2.75kW at 0.9m/s and 5C deltaT. You only need 3.5kW. Still at 5C deltaT that's only 1.2m/s, still within many recommendations. And you heat loss may anyway be (often is) a bit less than calculated.
So I would personally suggest to consider the 'suck it and see' approach, upgrading the rads for 45C and then running at the min flow temp you can given the pipework limitations. You can then decide whether to upgrade the one short length of pipework or not.
Or, if you can work out where that short length is, just upgrade the short length for the first 2-3 rads on the 15mm run.
What I definitely wouldn't do based on the figures you have given is upgrade all the pipework, its just not necessary. But, sadly, many heat pump installers love to do unnecessary work, funded by UK tax payers.
I have access to this part of the pipework under the small bedroom. In the picture hopefully you can see the 22mm flow and return pipes which go to the boiler in the garage. The 15mm pipes are in straight runs beneath the floor boards in the landing. I have yet to see how the 10mm microbore are attached to the 15mm.
I don't know what's achievable with pipework upgrades, but like you suggest, upgrading a short run of the 15mm where it's needed makes the most sense.
I have access to this part of the pipework under the small bedroom. In the picture hopefully you can see the 22mm flow and return pipes which go to the boiler in the garage. The 15mm pipes are in straight runs beneath the floor boards in the landing. I have yet to see how the 10mm microbore are attached to the 15mm.
I don't know what's achievable with pipework upgrades, but like you suggest, upgrading a short run of the 15mm where it's needed makes the most sense.
That's all very neat! If the 2*15 run in a straight line to the room next door to the right of the photo, and then the microbore tees off to the first 1-2 rads (which, without knowing the layout of your house, seems plausible), then you likely have just 1-2m of 'problem' 15mm pipe running in a straight line or with at most one bend, which in practice is unlikely to be a problem unless the area is particularly noise sensitive.
If its easy to take a bit of floorboard up where the relevant junction is likely to be, then I would do that, take a look and consider an upgrade of that length only. If it isn't easy to take that floorboard up, Id just run with it as it is and only consider doing something if it proves to be a problem. Likewise if 45C rads are a good physical fit, Id fit them.
You may need to do some gentle persuasion and/or show them the evidence to convince the installer. Several I spoke to wanted to upgrade my main 15mm cold feed to 22mm (which is a horrible job in my house), until I demonstrated the pressure of my mains (very high) and told them it simply wasn't going to happen.
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.
I've ordered a cheap borescope online and I'm going to have a look under the floorboards. I expect the order of radiators right of the photo will be: 1[hallway]-2[ensuite]-3[dining room]-4[kitchen]-5[bathroom]-6[main bedroom]. The 2x15mm run should be 5m long approx with no bends. Upgrading the run up to and including the dining room should be sufficient to reduce the demand on the remaining 15mm run below 2.75kW.
So three months later, we got our heat pump installed. We used an installer through Heat Geek who gave us a heat loss estimate of 4.1 kW and a recommendation for the 3.5kW Vaillant Arotherm Plus. He was made aware of the existing 15mm pipework, and as discussed already, the 2.75kW capacity of the 15mm was considered adequate.
So going ahead, our install consisted of: 3.5kw Vaillant Arotherm Plus, 200 litre cylinder, 45 litre volumiser, 45 degree design flow temp and corresponding upsized radiators. No changes to the existing 15mm and 10mm microbore pipework. Building details: Three bedroom detached two storey house, 88 sqm.
Our heat pump was installed right after the last cold snap in January, so we've yet to endure prolonged sub-zero temperatures. When it was 3 degrees outside, we were getting a COP of around 4.5. I've yet to see the flow temperature go above 40deg.
On the flowrate, I found a very informative thread on open energy monitor. It has been observed that the Vaillant's tend to run at the maximum flow rate and 'squeeze the DT' when adjusting the flow temperature. Knowing this, I was able to make sense of the flow rate readings from the live monitor. I typically get a flow rate of 780 l/h (0.21667 kg/s). Assuming that is the maximum flow rate the Vaillant considers optimal, that would mean I can expect a maximum heat output of 0.21667 x 4.2 x 5 = 4.55kW from the pipework, which exceeds the documented 4.3kW output at -3 degrees (@45deg design flow temp) from the heat pump.
I'm rather pleased with this outcome. It looks like we matched the right size of heat pump for our pipework. So here's a lovely photo of our brand new heat pump.
That looks good. I note the best practice of first fitting the pipe insulation and then clamping the insulated pipe to the wall - something that my installer didn't do. My 7kW Arotherm+ has a normal flow rate of 1200 litres/hour but I noticed it increased to 1800 litres/hour when heating the DHW. The latter may also apply for the CH in very cold weather (I didn't check).
ReplyQuote
Share:
Join Us!
Heat Pump Dramas?
Thinking about installing a heat pump but unsure where to start? Already have one but it’s not performing as expected? Or are you locked in a frustrating dispute with an installer or manufacturer? We’re here to help.
