I bought a Heat Pump

shinytop

Martyn1981 said:

Martyn1981 said:

Many thanks RR and Shiny. So if heating needs are low enough, my existing wet system might squeak through with a high temp HP in the coldest scenario, but it's always going to be a compromise then. Silly thought I had was that the smaller pipes might not effect efficiency, it would just take longer to heat the house ....... which of course means running everything for longer ..... which of course means less efficiency, doh!

I suspected that they would always be less efficient at a lower temp than a normal HP, but useful to get that answered.

Maybe it's silly to chase the last of the gas as it's reasonably low already, and just keep investing in RE schemes etc..

More pondering me thinks.

Blast from the past!

Been pondering this issue again, and looking into heatpumps again, possibly with the intention of replacing all the microbore in the house .... then I had a thought?

To get a heatpump sized appropriately, are the assessors allowed to take into account other existing heating, or is the system supposed to be sized to work in isolation?

Here's my thought - The one room in the house where heating is most likely to be inadequate during the worst couple of winter weeks we get, every 3 or 4 years, is also the one with a 3.5kW A2A unit. So even with sustained temps just under zero, it should manage a COP of 2(ish) and around 1.5/2kW of heating, which will be more than enough for topping up, without the need for a high temp heatpump.

As well as shoulder month use on PV, we have actually been using this unit overnight on E7 in the winter to help reduce GCH use. We put the temp to 18C, and leave the door half open.

Does that make sense? And I can't believe I didn't think of it back in April when chatting.

The assessor should look at the heat loss of the room with the A2A and work out how many watts it needs to heat to your chosen temp. You would end up with a smaller rad or none at all.  Despite what anyone says, it's not an exact science.  Although heat loss surveys assume separate rooms and closed doors, who keeps all their doors shut all the time (we don't!).  You could also fit a full sized rad and use a TRV to limit it when the A2A is on. 

It might get complicated if the installer needs to follow MCS rules for grant purposes.

The main issue with microbore is that the flow rate is limited, so the theory of high flow/low temp is harder to achieve. If you have to raise the flow temp to get the required heat output then efficiency falls.   

Martyn1981

shinytop said:

Martyn1981 said:

Martyn1981 said:

Many thanks RR and Shiny. So if heating needs are low enough, my existing wet system might squeak through with a high temp HP in the coldest scenario, but it's always going to be a compromise then. Silly thought I had was that the smaller pipes might not effect efficiency, it would just take longer to heat the house ....... which of course means running everything for longer ..... which of course means less efficiency, doh!

I suspected that they would always be less efficient at a lower temp than a normal HP, but useful to get that answered.

Maybe it's silly to chase the last of the gas as it's reasonably low already, and just keep investing in RE schemes etc..

More pondering me thinks.

Blast from the past!

Been pondering this issue again, and looking into heatpumps again, possibly with the intention of replacing all the microbore in the house .... then I had a thought?

To get a heatpump sized appropriately, are the assessors allowed to take into account other existing heating, or is the system supposed to be sized to work in isolation?

Here's my thought - The one room in the house where heating is most likely to be inadequate during the worst couple of winter weeks we get, every 3 or 4 years, is also the one with a 3.5kW A2A unit. So even with sustained temps just under zero, it should manage a COP of 2(ish) and around 1.5/2kW of heating, which will be more than enough for topping up, without the need for a high temp heatpump.

As well as shoulder month use on PV, we have actually been using this unit overnight on E7 in the winter to help reduce GCH use. We put the temp to 18C, and leave the door half open.

Does that make sense? And I can't believe I didn't think of it back in April when chatting.

The assessor should look at the heat loss of the room with the A2A and work out how many watts it needs to heat to your chosen temp. You would end up with a smaller rad or none at all.  Despite what anyone says, it's not an exact science.  Although heat loss surveys assume separate rooms and closed doors, who keeps all their doors shut all the time (we don't!).  You could also fit a full sized rad and use a TRV to limit it when the A2A is on. 

It might get complicated if the installer needs to follow MCS rules for grant purposes.

The main issue with microbore is that the flow rate is limited, so the theory of high flow/low temp is harder to achieve. If you have to raise the flow temp to get the required heat output then efficiency falls.   

Thanks. Yes fun meeting the MCS rules I suspect. Been looking at my EPC from 2012 and it suggests a heat demand of 15.5MWh (13,331kWh for space heating and 2,182kWh for DHW), but even including the gas oven our consumption was about 9MWh back then, but with a monster standout of 11MWh in 2013. Since then with other improvements it has dropped to about 7-8MWh through 2014 to 2020.

Since then closer to 6MWh, possibly 5.5MWh for this year, but the lower figures now reflect some use of the A2A units to reduce gas consumption.

It was a recent discussion* where I mentioned (and surprised myself) how low our average daily consumption of gas is in Dec, Jan and Feb, that set me off again looking at the HP idea, since unlike my earlier posts on here about a high temp HP, it occurred to me that our needs may be lower than an assessment suggests, plus the ability to boost heating from the front room A2A unit. Current rads are large double panel / double fin models, except that front room one that is more of a 'designer' type, so is naturally pretty rubbish as a rad.

[Just in case there's any confusion as I talk about having two A2A units, the original unit is in our tiny conservatory, and is ideal for adding heat in the shoulder months, but I'm not happy using it in the winter. I like to put it on when the sun has raised the room temp to, say, about 18C or more, then open the door into the living room with the A2A running off PV. When it's colder I feel I'd be using valuable RE gen to 'heat the planet' due to heat loss through the DG glass. Perhaps I'm being silly, but for these discussions I'm excluding that additional unit(?)]

My suspicion is that even with the microbore, a HP would work fine all year, most years, though may have to run for long periods, and the A2A 'boost' would cover exceptional periods, such as that 2013 period, but I don't know how such a package works for MCS/Gov box ticking.

*The tragic reality of energy independence!

Lastly, I don't require 30kW of heating, certainly not for a long period, as combi's (mine is a 28kW), are sized to meet instantaneous hot water demand, not long term heating. In the most recent Dec - Feb (and for HP shoulder months, when things are 'borderline' it's really early Q2 and late Q3/early Q4 we are talking about) we consumed approx 2,761kWh's of gas, for GCH, DHW and cooking (oven) or on average 30.68kWh's per day, or 1.3kW per hour (so to speak).

Obviously you will get exceptional periods of cold sometimes, but even if I take a negative guestimate from that winter consumption I gave of 2,761kWh's, and suggest 2,000kWh's just for a really bad January, then that's 'only' a daily heating need of 64.5kWh's (if the GCH is 100% efficient, and none of the DHW heat is lost down the drain), or 2.7kW's constant. [For background we have a classic (translates as 'bog standard') 1930's 3-bed semi.] 

shinytop

Martyn1981 said:

My suspicion is that even with the microbore, a HP would work fine all year, most years, though may have to run for long periods, and the A2A 'boost' would cover exceptional periods, such as that 2013 period, but I don't know how such a package works for MCS/Gov box ticking.

If the flow is a bit low the flow delta T (difference between leaving and returning flow) will be a bit high so your average rad temp will be lower for a given leaving flow temp. So yes may need to be on for longer.  You do need to be careful you can achieve the minimum flow for your chosen ASHP.  Mine will cut out if it gets too low and I think others are the same. 

matelodave

As shinytop says, you have to maintain a minimum flow through the heatpump otherwise it shuts down - the flow switch in mine heatpump shuts it off at around 16litres a minute. The heating circuit has a bypass to ensure that the flow rate is maintained when any of the zones are shut down.

The other thing to avoid is causing the heatpump to cycle, rather than for it to try and maintain a steady flow temp, starting & stopping reduces efficiency by quite a bit.

Reed_Richards

My heat pump has a buffer tank which sits below the hot water cylinder and is integrated with it so there is no visible join on the exterior.  The pipes to and from the heat pump to the buffer tank are 28 mm diameter.  I presume this is all to ensure that a minimum flow is maintained even with zones and TRVs on the radiators.   

markin

Martyn1981 said:

Martyn1981 said:

Many thanks RR and Shiny. So if heating needs are low enough, my existing wet system might squeak through with a high temp HP in the coldest scenario, but it's always going to be a compromise then. Silly thought I had was that the smaller pipes might not effect efficiency, it would just take longer to heat the house ....... which of course means running everything for longer ..... which of course means less efficiency, doh!

I suspected that they would always be less efficient at a lower temp than a normal HP, but useful to get that answered.

Maybe it's silly to chase the last of the gas as it's reasonably low already, and just keep investing in RE schemes etc..

More pondering me thinks.

Blast from the past!

Been pondering this issue again, and looking into heatpumps again, possibly with the intention of replacing all the microbore in the house .... then I had a thought?

To get a heatpump sized appropriately, are the assessors allowed to take into account other existing heating, or is the system supposed to be sized to work in isolation?

Here's my thought - The one room in the house where heating is most likely to be inadequate during the worst couple of winter weeks we get, every 3 or 4 years, is also the one with a 3.5kW A2A unit. So even with sustained temps just under zero, it should manage a COP of 2(ish) and around 1.5/2kW of heating, which will be more than enough for topping up, without the need for a high temp heatpump.

As well as shoulder month use on PV, we have actually been using this unit overnight on E7 in the winter to help reduce GCH use. We put the temp to 18C, and leave the door half open.

Does that make sense? And I can't believe I didn't think of it back in April when chatting.

A night storage heater seems the cheapest option.

Reed_Richards

With a suitably installed heat pump you can heat your house and your hot water at roughly one third of what it would cost with direct electrical heating (using a very approximate ballpark figure).  Economy 7 electricity costs more than one third the cost of day rate electricity so a heat pump should be cheaper to run than night storage heaters.  But the initial investment in a heat pump would be a lot larger.

Back to the original question, I suspect many assessors would view an air-to-air unit as air conditioning and not consider its heating potential.    

70sbudgie

Reed_Richards said:

With a suitably installed heat pump you can heat your house and your hot water at roughly one third of what it would cost with direct electrical heating (using a very approximate ballpark figure).  Economy 7 electricity costs more than one third the cost of day rate electricity so a heat pump should be cheaper to run than night storage heaters.  But the initial investment in a heat pump would be a lot larger.

Only just, my E7 night rate is now 37.5% of my day rate.

thefordprefect

@reed_richards or anyone else!!

we are about to have an ashp installed (Mitsubishi ecodan 11kW). The initial plan from the installer shows mitsubishi ftc6 interface and a couple of room temperature sensors.
We are "upgrading" from oil and a semi broken high efficiency boiler (now held together with chewing gum) replacing this and buying a years worth of oil at £1600 (£1/L) is only a few years oil price below having an ashp fitted (with £5k BUS grant)
This system has worked OK with a Wiser controller and 8 radiator electronic valves/thermostats. We would like to keep the system as it controls individual room heating as required. The wiser controller has weather compensation and will learn each rooms heating and cooling times adjusting the boiler on time accordingly.
However I do not understand how this would interface with the ftc6 controller

I believe you said you had a drayton wiser controller? If so could you please enlighten me as to how the Wiser connects to the ASHP to control heat demand.

We also have Myenergi Eddi to use excess solar to heat the domestic hot water. I believe this can be used with a heat pump by using the legionella output of the heat pump controller (power to immersion heater until legionella death temperature is reached) to feed the input on the eddi using a plug in board. The eddi then needs to be set to use boost output (i.e. not solar controlled) to water heater 1 when this added input is at 240v. 

Reed_Richards

Sorry to disappoint you but my Drayton Wiser cannot do Weather Compensation on its own account with my heat pump because there isn't a suitable interface.  I'm surprised it worked with your oil boiler; I thought it needed an Opentherm interface which is largely confined to gas boilers.  The good news is that the heat pump can do Weather Compensation on its own - well mine can and I'm sure yours will.

About a day after my heat pump was fitted a filter blocked and it would not operate.  At this point I found that I could not use my immersion heater independently of the heat pump so I could not get it to heat the water.  I found this unacceptable so got it rewired with a direct connection in parallel to the heat pump control box.  I don't have an Eddi (just an app controlled switch) but I can use this independently of what my heat pump is doing.  Therefore I don't need a plug-in board.

Oh, and welcome to the forum.