Air Source Heat Pumps

mikedain

richardc1983 wrote: »

If this is a small baby room I would suggest you make sure you size the unit up correctly as if you get too large a unit you will get uncomfortable drafts for baby and the unit will spend its time short cycling (switching on and off all the time) even though they are inverter there is only a certain margin they can ramp down to it wont remove much moisture if its too big a unit as it will be cooling too quickly even if ramped down.

3.5kws for a small room is very large. I would get the smallest unit you can find if its a very small room.

Where is the other unit situated?

Im looking for the smallest i can find ie around 7k btu or 9k btu for baby room.

other unit is in our bedroom

richardc1983

ah rite well i think the choice is yours, they are both in the same league of budget units, going by warranty if you had to take one back you would have to post back to ebay seller if it was from b&q you just take it back to b&q.

Frostybelgian

I have just built a house of 3000 square foot. It has concrete floors, insulated walls and roof, double glazing etc. We had underfloor heating installed with a 10kw PZP Air Source Heat Pump for the central heating and hot water with a 200 litre buffer tank - this was specified by the supplier who had a copy of our building plans and our SAP report. We moved in last November and have used over 31,500 kW/h of electricity at a cost of £3,500 - £500 to £600 per month during winter. The system does not cope with drops in temperature, during winter the hot water was not very hot yet we have massive bills. The supplier/installer now wants to install a gas boiler as a back up heat source rather than using the systems own electric elements. We have asked for our money back - no joy. Has anyone else had problems with these systems?

richardc1983

Frostybelgian wrote: »

I have just built a house of 3000 square foot. It has concrete floors, insulated walls and roof, double glazing etc. We had underfloor heating installed with a 10kw PZP Air Source Heat Pump for the central heating and hot water with a 200 litre buffer tank - this was specified by the supplier who had a copy of our building plans and our SAP report. We moved in last November and have used over 31,500 kW/h of electricity at a cost of £3,500 - £500 to £600 per month during winter. The system does not cope with drops in temperature, during winter the hot water was not very hot yet we have massive bills. The supplier/installer now wants to install a gas boiler as a back up heat source rather than using the systems own electric elements. We have asked for our money back - no joy. Has anyone else had problems with these systems?

A few people have reported these sort of problems, unfortunatly if you have it set on the system for a high flow rate temperature then the system just cannot cope, the max flow rate you will get by using just the heat pump is about 55-60C. Below freezing and this drops off quickly so it calls for extra heat from the electric elements.

THis has mainly affected from what I see people who use radiators and not underfloor heating as they didnt pay attention when they fitted the system to oversize the radiators due to the lower temp flow rates.

However underfloor heating works with lower flow temps anyway.

Maybe you need to look at disabling the electric heat and see if its warm enough without it, you might need to run the system for longer i.e have it come on at earlier for longer.

The very best way to make use of the current technology is by having air to air systems.

This means that the heat is distributed indoors via blowers or fan coils. This can also provide cooling in the summer.

I have this set up at home and it works very well, the house can be maintained at 26C if I want to when outdoor temps drop to -4.

I would also suggest you post this on the following forum engineers there will give you some proper advice for free.

Link here:

http://www.refrigeration-engineer.co...splay.php?f=78

The link is here, please use it I have passed a few people onto it on here and it has helped them a lot.

You will need to post the make and model of the system and what you have the flow temps set at etc.

Regards
Richard.

paceinternet

Frostybelgian, 3000 sq ft is about 300 sq m. This is a big floor area for a domestic property. It would be interesting to see how your installer sized the unit. If the insulation is very good as you describe, and no adverse location factors needed, an approximate guide would be that you design for 40 watts per sq m. which equals 12kw, plus hot water. You need to say how much hot water you use.
Maybe a detailed calculation gets you the 10kw, but often you need more than 40 w/sqm.
So first thoughts are that it is undesized and running with some auxiliary heating almost all the time.
Looking at the pzw web site you will see some performance data at different air temperatures when running at certain output temperatures. All systems have a reduced output at lower temperatures, but it depends on your model.
However, as an example, the 10SE model outputs are:
A7/W50 it is 9.2kw for 3.5kw input.
A2/W50 it is 8.1kw for 3.5kw input.
A-7/W50, it is 6.4kw for input 3.6kw.
HP3AWX model outputs are:
A7/W50 it is 9.7 kw for 3.6kw input.
A2/W50 it is 8.4kw for 3.4kw input.
A-7/W50 it is 6.9kw for 3.3kw input
These are ok heat pumps with respectable performance, but it shows you may be using the supplementary electrical heating for too much of the time.

richardc1983 tells a similar story, and I agree with his suggestion to try and switch off or disconnect the auxiliary heaters to confirm the performnce of the actual heat pump.
But I disagree that an air to air system is "the very best way to make use of the current technology". The efficiency of the heat pump is the same. The air to water system allows you to distribute the heat around a large area, and a number of rooms. If it was air to air, you would need multiple fan coil units and the energy used by the heat pump(s) would be similar.

My view is that it should be sized to run without auxiliary heating for an agreed number of days/hours per year. When this is correct, you can see that the cost of running a heat pump system is as good, or better than any other energy source.
Example: 358 days of the year when outside air temperatures are above say -7 degC.
For 7 days of the year some extra input from electrical heaters can supplement the system, example 4kw for 168 hrs, an extra 672 kwh at £0.10 per kwh = £67 per year.
Or whatever you feel is the right balance versus the extra capital cost of a larger heat pump system.

Frostybelgian

Hi, thank you for your response,yes it is a big house, there are five people having showers and all ancilliary water usage. During the winter months the water produced was not hot enough to have a bath in. The unit was supposedly sized for the property using the SAP calcs and it is is an HP1AW 10SE-2AG, the power input is listed as (A2/W35) - 2.5kW, the Ph is 8.9kW the COP is 3.6, Max Power Input 8kW, Max Total Power Input 11.8kW. The heating elements were on most of the time during winter and we werer struggling to keep the house warm, 21C in living areas 18 in beds. We have the CH output at 35C, the spacing of the underfloor heating pipes is 100mm to allow for lower output temperature.

paceinternet

http://www.pzp.cz/en/products/heat-pumps/heat-from-air/air-_-water-split-systems/

http://www.pzp.cz/_dataPublic/downloads/29f515cab913b330020f0a3d8bffcc17/Split_EN.pdf

I think you are confirming what we have said. It is undersized and it is not the fault of the heat pump. It is described as having 8kw of electro boiler as standard, with max possible of 14kw. If an additional 8kw has been running on your system and overall still not providing adequate temperatures, you can see you have some way to go!

How do you move forward from here?
Do you want to build a case to claim from the installer?
Or get on with a solution to sort it before next winter?

Out of interest, is the hot water working ok now in the summer months with no heating requirement?

You should ask for a review of the design power needed for the heating system, and separately, the hot water.
Consider if the heat pump can run a zoned area adequately, and either add into the system another heat pump or a gas fired boiler.
You should be able to run your underfloor at a higher temperature than 35 deg C, but maybe ask what room temperatures could be achieved at what water temperatures at outdoor winter temperatures.

Frostybelgian

The hot water is working ok now with no heating requirement.

I need to build a case against the installer to sort this out properly and then find the best solution before winter.

How do you calculate the heating reuirements for a building, I have done a rough estimate for a gas boiler and the house seems to require something near to a 32kw boiler - how can this compare to the heat pump?

richardc1983

Frostybelgian wrote: »

Hi, thank you for your response,yes it is a big house, there are five people having showers and all ancilliary water usage. During the winter months the water produced was not hot enough to have a bath in. The unit was supposedly sized for the property using the SAP calcs and it is is an HP1AW 10SE-2AG, the power input is listed as (A2/W35) - 2.5kW, the Ph is 8.9kW the COP is 3.6, Max Power Input 8kW, Max Total Power Input 11.8kW. The heating elements were on most of the time during winter and we werer struggling to keep the house warm, 21C in living areas 18 in beds. We have the CH output at 35C, the spacing of the underfloor heating pipes is 100mm to allow for lower output temperature.

U see this is why I think fan coils units are better, you have a unit mounted on the wall but because of the airflow you have in affect trebled the surface area of the unit so your building heats up quicker and stays warmer for longer as underfloor heating relies on convection and radiant heat.

paceinternet

Frostybelgian wrote: »

the house seems to require something near to a 32kw boiler - how can this compare to the heat pump?

If the heat pump itself can produce 8.9kw at A2/35, plus the 8kw of direct electrical auxiliary heat, you have 16.9 kw available. Although the auxiliary part may well be able to contribute the 8kw at a higher temperature useful for the hot water.
Obviously, this is only around half the 32kw you think you might need.

Also, I hope you recognise that the heat pump part of the heat input when operating at a COP of 3.6 will be costing less than 3p per kwh. The direct auxiliary heat will be costing around 10p per kwh. And a modern efficient mains gas boiler will be costing around 3-4p per kwh, all depending on your tariffs.