ASHP installed together with existing heating system

[joe90]

21 minutes ago, SteamyTea said:

I added insulation around my cylinder, saved a couple of kWh a day.

Also if the DHW temp is lower, the heat loss from the cylinder is lower.

[Bruno]

14 hours ago, joe90 said:

Why?, I heat my DHW to 48’ and cannot hold my hand under the hot tap or shower at that temp (and I like it HOT). Why would winter make any difference, the COP might be slightly less (reliant on RH rather than temp)

As I said before, mostly due to the cold sensation in the bathroom. And according to your descriptions, It seems clear that I have significant losses in the pipes, I definitely need to improve that.

 

14 hours ago, SteamyTea said:

If you take the showers at about the same time, there is no need to recharge until a bit before it is needed again i.e. early morning

That's how we use it now, with the wood burner: we start the fire, the cylinder gets hot, everyone showers, the cylinder gets cold. Tomorrow we heat it again. That's how I intend to keep it even with the heat pump.

 

[J1mbo]

You might find that the DHW is not material enough to bother with timed programmes, relative to the convenience of having it always it always hot.

[Bruno]

True that. I guess we'll see, for sure I'll try both ways. First I need to find an installer who wants to take my money ?

[jack]

17 hours ago, Bruno said:

- on one side, my wife and kid love to shower with water which makes their skin turn red ?

 

The pain threshold for water immersion is 41-42°C. Believe me, 50°C is unbearably, scalding hot, I don't care how cold the bathroom is or how hot they think they like it!

 

I used to run our DHW at 55°C (the max our ASHP heat pump can output). However, I turned it down to 50°C as an experiment, and there's no practical difference.

[Bruno]

On 20/03/2021 at 18:52, J1mbo said:

Although they have their own cylinders, any heat pump cylinder would do - the coil surface area is larger than standard cylinders. Typically 3m2 or more.

OK, some further updates, I was able to get in touch with the manufacturer of my DHW cylinder.

According to them, it's a 150l copper cylinder, with a 10m copper coil, inside diameter 22mm.

 

That gives roughly 15m of water volume, but only 0,7m^2 of surface area, although it's copper which has greater conductivity. In fact, the cylinder does heat up quite fast with now, so on that part it's not an issue.

If I add 3m of external connections, that goes roughly to 20l of water for the DHW circuit. Do you think that this is enough for the heat pump to work? The minimum flow indicated on the specifications is 540l/h.

Edited March 25, 2021 by Bruno

[Bruno]

18 minutes ago, jack said:

The pain threshold for water immersion is 41-42°C. Believe me, 50°C is unbearably, scalding hot, I don't care how cold the bathroom is or how hot they think they like it!

I didn't know that, but it seems clear from your (and others) previous comments that I have very significant heat losses from the cylinder to the shower. I will have to work on improve that for sure.

[Bruno]

Just a quick update to this topic as I got my brand new Vaillant aroTHERM plus 85 installed and started up yesterday and today. 

 

I was able to get the installation as I wanted, including the possibility to use the wood burner together with the heat pump. 

I'm waiting for the "Internet gateway" VR920 to be able to access the system from the Vaillant app. 

 

I got the VRC700 controller, which is a bit "outdated" if I'm honest. Not having a color LCD in 2021 as a minimum is really strange... I was hoping to get the sensoCOMFORT VRC720 but the price is a bit high. Anyway it serves the purpose and now I'm starting to take some daily registers to improve overall efficiency. 

[Dan F]

On 20/03/2021 at 18:52, J1mbo said:

If you're in the UK and looking at RHI, it's worth playing with the design flow temperatures (even if this means changing some radiators) as lower flow temp = higher COP from the MCS product performance tables = higher payments.

 

How does this work, the installer just declares a design flow temperatuere in the MCS submission?

[Dan F]

10 minutes ago, Bruno said:

Vaillant aroTHERM plus 85

85?  8.5kW?  We were offered 7kW or 10kW.]

 

Out of interest:

- Did you have hydraulic module installed or the decoupler (with built in buffer tank).

- What approach are you using for controls? Vailant controller + "functional module"?

[Bruno]

Yes, mine is a 8,5kW unit. I can get you the correct model tomorrow if you want. 

 

No, I don't have the hydraulic module. I have a 3-way valve for diverting the pump output to DHW tank/buffer tank + radiators. 

These are all "non Vaillant" components.

The controls are all Vaillant: first is the "base" controller which receives the temperature probes, controls the circulating pump and 3-way valves, and also includes a wireless EBUS module which allows the usage of an external temperature and humidity sensor. Then the VRC700 controller which serves also as room temperature sensor.

Edited April 20, 2021 by Bruno

[Dan F]

19 hours ago, Bruno said:

Yes, mine is a 8,5kW unit. I can get you the correct model tomorrow if you want. 

 

No, I don't have the hydraulic module. I have a 3-way valve for diverting the pump output to DHW tank/buffer tank + radiators. 

These are all "non Vaillant" components.

The controls are all Vaillant: first is the "base" controller which receives the temperature probes, controls the circulating pump and 3-way valves, and also includes a wireless EBUS module which allows the usage of an external temperature and humidity sensor. Then the VRC700 controller which serves also as room temperature sensor.

 

Realized you are in Portugal (?).  I think it's probably the same one that is marketed as 7kW in the U.K.

 

If you look at the Vaillant schematics [1] there are about 6 different options

- Buffer only

- HEX. and Buffer

- HEX. only

- Hydraulic Station and Buffer

- Hydraulic Station, HEX and Buffer

- Hydraulic Station and HEX

- Nothing

 

Which setup do you have?  @J1mbo which setup do you have?

 

[1] https://www.vaillant.co.uk/downloads/aproducts/renewables-1/arotherm-plus/all-schematics-wiring-notes-1799366.pdf

 

[Bruno]

First one, buffer only

 

My first real complaint, the display always shows setpoint and actual heating temperature, even if heating is disabled as it is now. I'd like to show easily the DHW temperature, but it's only buried in the technician menus.

 

Other than that, a quick test shows that my radiators do heat up nicely (energy consumption will be checked only next winter). Also the DHW is amazing. 1,5kWh from the grid to heat the tank in 45min. Before with the resistor it would take at least 5h and some 6kWh. I did choose a favourable hour of the day (14h so better COP). The tank should lose some temperature until it's time for shower, but I programmed it for a little boost after dinner time. 

[Dan F]

3 hours ago, Bruno said:

First one, buffer only

 

Vailant buffer?  Glycol for ASHP-Buffer loop?  Your own 3-port value for CH/DHW control?   Is a Vaillant heat pump interface controlling 3-port valve?

 

I'm trying to get my head around it, sorry! Our schematic has a hydraulic unit and I've no idea what it does.   I assumed we just needed a buffer and that the buffer serves to decoucple ASHP and heating circuits anyway.  Yet there are schematics that use buffer+heat exchanger+hydrualic unit!!

 

[Bruno]

1 hour ago, Dan F said:

Vailant buffer?

Nope, standard "after market" buffer tank. 100l as we couldn't get an affordable smaller one. 

 

1 hour ago, Dan F said:

Glycol for ASHP-Buffer loop?

Yes

 

1 hour ago, Dan F said:

Your own 3-port value for CH/DHW control?   Is a Vaillant heat pump interface controlling 3-port valve?

Yes to both 

 

1 hour ago, Dan F said:

Our schematic has a hydraulic unit and I've no idea what it does.

For what I've been told, it serves to couple different heat sources together (eg heat pump and solar), with much less amount of water (therefore inertia) compared to a buffer tank. It also isolates the ASHP from the heating circuit so that you don't have to empty all the circuit (thus spending Glycol and lots of water) every time you need to do maintenance. But the buffer tank also does that. 

 

1 hour ago, Dan F said:

the buffer serves to decoucple ASHP and heating circuits anyway

That's actually messy. According to Vaillant, you need a buffer tank to perform defrost. When the heat pump needs do defrost it will fetch heat from the buffer tank so that's why it needs it. In the installation manual it mentions different buffer capacity according to the heating circuit temperature: lower temperature --> bigger buffer, higher temperature --> smaller buffer. It can be as small as 20l IIRC. 

Nevertheless, pretty much all installers here use the buffer tank (in Portugal defrost is not really a thing ?) as a way to stabilize the temperature fluctuations in the heating circuit: it's actually called an "inertia tank" and not "buffer tank" and the thumb rule is 10l per kW. I'm guessing that most heat pumps are very oversized (I got quotations for 15kW units!), therefore the additional mass of water helps to stabilize the temperature in the circuit as a way to preven short cycling. From the little I observed the aroTHERM working I'm pretty sure that it would be able to run my central heating without any buffer at all (but I'm just guessing though).

 

But I have a neighbour with a 14kW LG and no buffer (also no DWH just CH) and that pump is always, always short cycling. I'm pretty sure that it's extremely oversized so the buffer tank would help greatly. Also, the aroTHERM allows you to adjust the heating curve and the LG Therma V doesn't. In my short tests that parameter greatly influences the slope of the power output of the heat pump, in his case the LG pump starts and a few minutes later is at its maximum power, which is also not good for the short cycling issue.

Edited April 21, 2021 by Bruno

[Bruno]

Here's a picture taken during installation. Sorry about the mess :) 

You can see the buffer tank, the 2 3-way valves (on the right of the tank) and the circulating pump (on the left). Further on the right there's the Vaillant controller which receives the temperature probes and feeds the valves and circulating pump.

 

It's not on the picture but to the right of all that there's the DWH cylinder.

[Dan F]

So you have the setup on  "page 3" of: https://www.vaillant.co.uk/downloads/aproducts/renewables-1/arotherm-plus/all-schematics-wiring-notes-1799366.pdf. For some reason this doesn't show any glycol circuit though.

 

I think I get the "Hydrualic unit" now, it's basically the  heat pump interface + 3-port value + pump + optional backup heater in a single box. Kind of makes sense if you want to reduce "bits" but not needed as such.

 

I've stil no idea what the "Heat Exchanger" is though or why you would use one.  It does seem, from looking at Vaillant schematics, that they only using glycol when there is a heat exchanger (seperate to any buffer tank) though..

 

[Bruno]

Yes, the hydraulic unit is an "all in one" solution from Vaillant. It's integrated and uses the Ebus as well. 

The heat exchanger is also called hydraulic separator. On the first page of this topic someone explained it very well. But basically it's a plate exchanger which transfers heat from one or more circuit to another. 

 

As for Glycol it's a corrosion inhibitor which should always be used in combination with aluminium radiators. It also affects the freezing (or was it boiling?...) point of the water, which is why it's only used on the "inside" portion of the circuit: you don't want water with Glycol running through the heat pump

Edit: again, this is what I've been told 

Edited April 21, 2021 by Bruno

[SteamyTea]

12 hours ago, Bruno said:

Before with the resistor it would take at least 5h and some 6kWh

That implies that you had a 1.2 kW element in it.  That is very small.

Edited April 22, 2021 by SteamyTea

[Bruno]

I need some further advice on 2 issues, both related to the installation.

 

- insulation of the pipes and connections. Although the installer was very careful in distributing the pipes on the wall to reduce "dead space", I'm a bit concerned about insulation.

All pipes have an external insulation sleeve, which is the same on the inside and outside. But all connection parts (especially 90º metallic - brass? - curves) are not insulated at all. Outside, there are 2 of these curves. Inside, around the 3-way valves there is big "set" of metallic parts which are all exposed and do heat up a lot when the heat pump is working.

Isn't this something which might represent significant heat losses especially in winter? Do you have any recommendation for better insulation, or shouldn't I be worried?

I did ask the installer about this, he claims that this is the standard way of doing it.

 

- vibration noises in the structure

The heat pump was mounted on the wall as I cannot put it on the ground. During the night when everything is silent there is an audible humming noise which seems to come from the structure of the house. Although this seems to be a frequent problem, it's something that never came up in all the previous reading and research I did. The solutions I found out now are some rubber pads, but I would like to ask if someone already encountered this issue and which kind of pads are the safest bet in fixing this problem?

I discussed this with the installer, we will go ahead and do a first test with a small rubber piece just to check if there is some improvement.

[Bruno]

Any thoughts about these issues? Thanks

[Nickfromwales]

Assuming the heat pump is bolted to a frame, and the frame is bolted to the building?

Then;

These for each of the 'feet' of the heat pump and go from there. If that reduces but does not solve the problem, then look at similar to separate the frame from the building.

and;

This stuff for insulating anything that doesn't need any regular disassembly.

[dpmiller]

There are flexible hoses between the ASHP and the pipes in the wall?

[Bruno]

5 hours ago, Nickfromwales said:

Assuming the heat pump is bolted to a frame, and the frame is bolted to the building?

Yes, it is. Thank you, I actually have access to these rubber pads for free ? Will try them shortly.

1 hour ago, dpmiller said:

There are flexible hoses between the ASHP and the pipes in the wall?

No, there aren't. It's just 3 sets of 90º curved sections.

 

Here's a picture which shows both the tubing and the wall mounting

Edited April 28, 2021 by Bruno

[Marvin]

Hi Bruno

I would insulate the pipes as much as possible. It will do no harm and only help. I wouldn't worry about industry standard, only a better standard. The only thing I would say is to avoid insulation around electrical parts like the box on the port valves next to your tank.

 

Marvin