Heat pump / inverter DIY

stevehead

megohm wrote: »

Has anyone experience of mounting at say 600cm - 1m from the floor? Obviously the breeze hitting you in the neck if seated nearby could be a problem, but anything else?

Well, they do stick out quite a bit.
The heat can be directed straight down so no windy neck.
Can you get the pipework there from under the floor; you have to consider the route from the indoor unit to the outdoor unit with a maximum pipe length of 15m.

richardc1983

megohm wrote: »

New to this forum but considering the Mitsubishis. Currently on full electric and using around 5-6kW with the -3 outside at present (a large 3/4bed detached but well insulated!).

Problem is I don't want them high on the wall as usually recommended. I know I could use floor units, but they're a lot more expensive. Has anyone experience of mounting at say 600cm - 1m from the floor? Obviously the breeze hitting you in the neck if seated nearby could be a problem, but anything else?

The high wall units are designed to be high wall due the airflow direction from them. Low floor units send the air spiraling up out the top of the unit and across the ceiling and this avoids cold draughts in cooling, heating mode they will distrbiute it towards the floor.

The high wall units (cheaper) distribute the air differently. Air flow comes from the bottom of the unit, In cooling the units throw it across the room over head height (hence the high ceiling reccomendation) this will be a blanket of cool air that gradually falls cooling the room. If you dont mount them at that height you will have probs as the units will be throwing ice cold air straight across at you which would feel very unpleasant, heating mode you prob wouldnt have too many probs with as the units direct the airflow downwards towards the floor although the angle of air flow again may cause problems.

What is stopping you from mounting them in their recommended position? There going to look more odd mounted 1mtr off from the floor as floor units are mounted lower than this.

I am going to sleep now as work night shifts so will check for your response after.

There are a few HVAC engineers reading the thread who will prob back me up.

Regards
Rich

richardc1983

stevehead wrote: »

Well, they do stick out quite a bit.
The heat can be directed straight down so no windy neck.
Can you get the pipework there from under the floor; you have to consider the route from the indoor unit to the outdoor unit with a maximum pipe length of 15m.

Theres a prob with this though steve, in heating warm air will find its level and rise up from the floor... all good u say.

IN cooling however, if your directing the airflow downwards, your going to end up with a very cold floor area as the cold air is going to stay at floor level and not mix with the rest of the room air, so you will have probs with temperature control!

megohm

Thanks for your responses.

No problem with accessing under the floor, indeed its usually easier as its an upside down house with living accommodation on the first floor.

Positioning is partly the above and partly looks. In most of the available positions a high wall mount would look pretty intrusive. I have some spaces lower down that would be less so.

I take the point about cooling. However up here in the NE that might only a problem for a small part of the year.

rothers8080

I've got the monitor on my cheap inverter unit now and it's using between 500w 700w to keep the open plan (living, dining, kitchen) 23 degrees. It's 1-3 degrees outside right now.

It was -6 yesterday and we thought it would be struggling when we got in, but the room was toasty warm although it was pulling between 900w and 1300w to keep it there. But that's the first time we have been under -5 this winter in waking hours.

I'm very happy with this for £475 all in, as Steve said warm weather is coming back tomorrow, 10degrees predicted here, should be interesting to see the power usage then.

alicelight

I've been following this thread with interest and wondered if any of you could help me, as I'm a bit lost. I want an air to air heat pump for my 49m2 log home, to be built in Cornwall.

The building is fully insulated and double glazed etc and I've been told they don't require much heating at all due to their construction (someone near me recently put in a solid fuel burner in theirs and is roasting!). We're not on mains gas and I don't want oil or LPG... can't afford other renewables, so it's looking like ASHP might be the way to go.

We've got around £1,000 to spend, including installation. I'm not sure whether to do this ourselves (bit daunted by the pipework and refrigerant), what btu would be suitable, what manufacturer or where would be the best place to put it internally for the best airflow. Don't mind opening bedroom doors in evenings for some warmth, or using little electric heaters occasionally in them, if required.

I'm keen on Mitsubishi Heavy Industries unit, but I heard that the smaller units aren't anti-corrosion, which may be a concern in such a salty and damp area like Cornwall, so Daikin has also been suggested to me.

Here's a link to a rough plan of the 6m x 8m build (sorry it's so small). The glass to the south (plan is oriented east to west) is a glass patio door set and 2 x full length picture windows. In the open plan area there's a vaulted ceiling to 3m high, with a 2.5m flat ceiling in the bedrooms:

www.birthsupport.org.uk/build.html

Just want to know really if this is this feasible for the £1,000 budget, or if I'm dreaming?! Thanks for any advice in advance...

mech_2

stevehead wrote: »

So lets pretend all ashp are born equal and deliver an average COP of 3 during the 6 month heating season. Cost per Kw, this would be on parity with gas. And let's estimate that by using either ashp or gsh you use £30 worth of energy per month. The heating bill for the 6 months is then £180 for either system.

But my point from the beginning has been that all these assumptions are all very well, but they're not based on any checkable figures. The costs are probably fairly similar either way (leaving aside cooking and hot water), but to be certain we need proper seasonal figures.

But then we have to add
£24 (gch elec cost) + £176 (eon gsh service contract) = +£200 annual overhead
or
£24 (gch elec cost) + £76 (est RGI service) = +£100 annual overhead

Therefore the total annual running costs of a new Gas Combi are 50 - 100% higher than ashp.

Oh come now. You're just grasping at strawmen. I don't have any kind of service contract for my boiler. I don't believe them necessary or useful for a room-sealed boiler. If I notice it doing something unusual I would get someone in for a one-off cost just as you will when the fan bearings wear out on your ASHPs or something.

Annual service of ashp is a diy job that consists of simply cleaning the crap out of both units.

I dare say most people would still sign up to a service contract though.

ASHP doesn't overshoot; it doesn't have 50 gallons of useless hot water to dissapate if the sun comes out.

A house with an ASHP would overshoot if the heat supplied by the sunshine was greater than the house's heat loss. It's quite likely April/May/Sepember/October when the heating load is low. If the heating load is low, the likelyhood is that radiators wouldn't be hot anyway.

Right now I can see that my boiler is set to a temperature of 66 degrees C. The return water temperature would be roughly 10 degrees lower than that. This is quite high by my standards. I've turned it up because it's the middle of winter. It doesn't have weather compensation.

Using the rule-of-thumb of 10 litres per radiator, a 9 radiator system would be about 20 gallons. 20 gallons of water at an average temperature of 60 degrees and a room temperature of 20 degrees would contain about 4.2kWh. It might be possible to get an extra 2kW through south facing windows on a sunny day. Let's say it keeps this up for half an hour constantly while the radiators cool down close to ambient. That's only 1kWh more than the thermostat expected. That's probably enough to make my house overshoot by 0.25 degrees C. I'm not even going to notice it. Additional heat loss for the day might run at 0.2%. Less for the whole heating season as most days are not particularly sunny.

Unless the discussion is based on some realistic figures, it's all just shooting in the dark.

thechippy

alicelight wrote: »

I've been following this thread with interest and wondered if any of you could help me, as I'm a bit lost. I want an air to air heat pump for my 49m2 log home, to be built in Cornwall.

The building is fully insulated and double glazed etc and I've been told they don't require much heating at all due to their construction (someone near me recently put in a solid fuel burner in theirs and is roasting!). We're not on mains gas and I don't want oil or LPG... can't afford other renewables, so it's looking like ASHP might be the way to go.

We've got around £1,000 to spend, including installation. I'm not sure whether to do this ourselves (bit daunted by the pipework and refrigerant), what btu would be suitable, what manufacturer or where would be the best place to put it internally for the best airflow. Don't mind opening bedroom doors in evenings for some warmth, or using little electric heaters occasionally in them, if required.

I'm keen on Mitsubishi Heavy Industries unit, but I heard that the smaller units aren't anti-corrosion, which may be a concern in such a salty and damp area like Cornwall, so Daikin has also been suggested to me.

Here's a link to a rough plan of the 6m x 8m build (sorry it's so small). The glass to the south (plan is oriented east to west) is a glass patio door set and 2 x full length picture windows. In the open plan area there's a vaulted ceiling to 3m high, with a 2.5m flat ceiling in the bedrooms:

www.birthsupport.org.uk/build.html

Just want to know really if this is this feasible for the £1,000 budget, or if I'm dreaming?! Thanks for any advice in advance...

Alice,

I've carried out the heat load calculation for you and it comes in around 4.8kw. Due to the vaulted ceiling in the central section, I'd allow for a 6kw system.
The condensers on most outdoor units these days are corrosion proofed, but I'll try to find out for you. Both Daikin and Mitsi are good - I prefer Mitsi personally.

I know Craig is happy with his self install system and fair play to him, but I would not go that route. Should it go wrong, the technical and spares backup is appalling to say the least. It has been illegal for some time to install a system yourself, UNLESS, as Craigs, it has pre-charged refrigerant lines. However, due to increasing pressure from the refrigeration industry, the self install systems may disappear soon.

As for price - £1000 installed is pushing it a bit. £1200 would be more realistic, but that depends on the engineers in your area. A good quality install (as with central heating) will make a huge difference in system reliability.

Any more questions - please feel free to ask.

G.

richardc1983

My system today in 10hours has cost £2 to heat the flat to 22C.

I usually only have one unit on but one unit uses about 1.2kw per hour to keep the whole flat warm and at 22C setpoint. Total output of the unit is 4kw at a push when on Turbo mode.

@CRAIGX can you tell me what the rated output of your unit is?

Regards
Rich.

stevehead

mech wrote: »

But my point from the beginning has been that all these assumptions are all very well, but they're not based on any checkable figures. The costs are probably fairly similar either way (leaving aside cooking and hot water), but to be certain we need proper seasonal figures.
<<Snip>>
Unless the discussion is based on some realistic figures, it's all just shooting in the dark.

The problem with taking that stance is that there simpy are no figures available that make for a universally satisfactory comparison. There could be years to wait before the various organisations & manufacturers agree and produce such a standard.
That leaves with only 1 thing - user feedback. This thread is a testiment to how flawed that is as a method for assessing the true capabilities of ashp's.
In the meantime, you could be missing out if something really good comes along.

Something we haven't touched on but is bound to arise in TCO (cradle to grave) discussions is the durability and lifetime of boilers vs ashp - another stick to beat ashp with? Oooo.. they haven't been tested to a common standard....it never ends.

mech wrote: »

Oh come now. You're just grasping at strawmen. I don't have any kind of service contract for my boiler. I don't believe them necessary or useful for a room-sealed boiler. If I notice it doing something unusual I would get someone in for a one-off cost just as you will when the fan bearings wear out on your ASHPs or something.

Those aren't straws, they add up to a huge proportion of the running costs. You can't ignore the electrical consumption 'cos to me that's a whole months worth of heating.
Secondly, I thought the consesus here at MSE was that the annual gas service check was essential, or am I mistaken? Well that's not free either so you can't simply ignore it - another 2 or 3 winter months heating cost for my ashp's.

A business might get a service contract for ashp's for the same reason that they get contract cleaners in, but why at home? I wouldn't have my fridge or freezer annually serviced, but I would clean them myself. No cost.

mech wrote: »

Using the rule-of-thumb of 10 litres per radiator, a 9 radiator system would be about 20 gallons. 20 gallons of water at an average temperature of 60 degrees and a room temperature of 20 degrees would contain about 4.2kWh.

OK I'd mis-Googled the capacity of GCH systems and calculated about 10Kwh for a 40C drop. I'm just trying to figure out why heating using wet rads and a gas boiler is costing so much even with all this A rated stuff. Everyone from these boards to friends to the media are bandying around high heating costs - something I don't suffer from any more.
If anything I say on a public forum results in even just one person adopting this technology then as far as I'm concerned I 've done the world a favour.
ANdd time for another glass of vino... sorry if that's a bit of a blurt