A Heat Pump to Keep you Warm

A Heat Pump to Heat the House

So you take all this time and money and make your home super insulated. You make it so energy efficient that you can remove your oil boiler and your baseboard heating. What do you replace it with?

My answer is an Air-to-Air Heat Pump. What is that?  A heat pump uses the same technology as an air conditioner or a refrigerator. The basics are that you compress a gas (refrigerant R410a or similar) to a liquid which gives off heat. You also let this liquid evaporate to a gas which takes in heat (gives off cold). If you want to heat your house you capture the heat part of this circuit. If you want to cool your house you can capture the cold part of this circuit.

Think of your refrigerator. Inside it is cold (the expansion part of the process) the back of the refrigerator is hot (the compression part of the process). The heat pump uses the same process.

Heat pumps are also super efficient. They take 1 kilowatt of electricity and make 2.5 kilowatts of heat. How can it do that? It uses the relative heat of the air (up to -18F) to boil that refrigerant. That is free 'heat' from the outside air. That is how it gets more heat out of 1 kW than 100%. These units are 250% efficient!

You see in the picture above the outside part of the system. This type of system is called a mini-split. It is a split because the condenser and evaporator are in separate places. Here is the inside unit.

The wall around it isn't finished just yet but it will be soon. 

With the system as I have designed it, based on super insulated houses in Vermont, the warm air blows into just one room. This moves through the house using natural air flow. But natural air flow isn't enough to do a really good job of distributing the heat. We are also using a Heat Recovery Ventilation system (HRV). This HRV is a marvel of modern building science.

Here is the HRV. It isn't ready yet. I'm still 

installing it. When finished it will save on

heating costs.

It draws warm but stale air out of the kitchen, bathroom and mudroom and transfers the heat from this air into the cold but fresh air from outside. It does this at an efficiency of 85%! This means when you put 0F outside air into the HRV and you have 70F inside air the fresh air comes into the house at 59.5F! 

If you are getting fresh air in your house at 59.5F then your heating system needs to warm it up just 10F instead of the 70F you would need to warm it up if it was coming in at 0F!

Thus a smaller heating system can heat your house.


Short Cycling

One issue that some point-source heat pumps in super energy efficient homes have been having is short cycling. This is when the heat pump turns on and off many times each hours. It is bad for a heat pump to do this. It decreases the efficiencies of the heat pump and causes wear and tear on the compressor, shortening its life.

Peter Schneider, senior energy consultant at Efficiency Vermont, found that the heat pumps in the homes he was working on were short cycling. He found this out because he was/is monitoring these houses. Each system has monitors on them showing when they are on, hoe much energy they are using and their efficiencies. 

Data monitoring is a great way to see how a house is performing. Peter was able to determine that the heat pump was short cycling by looking at the monitoring data on the heat pump. What he discovered was that the inside unit of the heat pump has a temperature sensor, a thermostat just like the one on the wall in your living room. If the room it is in gets to the set temperature it turns off. Once the heat leaves the room (migrating to other parts of the house) it turns back on.

The solution for this was to move the thermostat from inside the room the unit is in to a distant room. The heat pump then stays on until that room is at the set temperature. Since it takes longer for the heat to reach that room the heat pump doesn't turn off and the short cycling stops, protecting the compressor and keeping the efficiency of the heat pump high.


When can I use a heat pump?

You can put Air-To-Air heat pumps into any house. Just make sure that you have a good idea of how much heating your home needs and to have enough heating capacity (large enough heat pump or multiple heat pumps).

Do I need a well for a heat pump?

It depends on which type of heat pump you choose. 

There are two main types of heat pumps. Most people think only of the ground sourced heat pump. These are very efficient units but are quite costly to install. They use the relative heat inside ground water. Therefore you need to drill wells (or use your water well) and a distribution system in your house like radiant floor heating or low temperature radiators.

The second type of heat pump is the air-to-air heat pump. This doesn't require wells or a distribution system (radiant floor or radiators). It just blows warm air into the house. 

Air to air heat pumps are by far the cheapest option for new homes. If they are super insulated homes you can use a heat pump with a very low output. 

Some Passive Houses have an air-to-air heat pump with only 9,000 Btu/hour output. To put that into perspective a 2000 sq ft home built to Vermont Residential Energy Code needs a 120,000 Btu/hour boiler! That is a 92.5% reduction in the power of the heating unit!

Deep Energy Retrofit Blog moving to Blogger for ease of use

I have been blogging about my passion for super energy efficient homes for the past year and a half or so. Up to now all of my blogs have been self built on my website www.ecohousesofvt.com. I have put lots of time into formatting and uploading, etc. I would much rather use this time to actually work on projects and write/broadcast about them.

For those of you who are just starting to follow this blog I will spend a bit of time on the background story. 

My name is Chris West. I am pushing 50 and have been fascinated by the energy we use to heat and cool our homes for years. In 2010, I returned back to the US after spending 10 years living in the Netherlands (Holland) where I got a Bachelor's in Science in Mechanical Engineering. While in the Netherlands I spent time working towards a better understanding of how buildings work and how we use energy in our buildings. 

Upon returning I decided to get certified as a Passive House Consultant. Passive House is the most energy efficient building standard in the world. With the thoughtful application of modern building science we now have at our disposal the tools to make homes that use almost no energy to heat or cool. A big step in the right direction.

When I moved to Northwestern Vermont in 2010 I bought a rather simple house. It is a 1976 raised ranch pictured here with someone else's dog. This is what it looked like when I bought it. It 'ticked all the right boxes' as they say in England. Not to far from an airport or hospital yet secluded, in the woods. Not a beautiful house but more than enough for me, my wife and two kids. 

I was in for a big surprise when we had our first Winter. Not because we were taken aback by the cold, we know Vermont and were expecting it to be cold and even like the cold. No, it was the amazing amounts of fuel we needed to burn to keep the house warm, and this was before heating oil hit $3.95 a gallon.

There are many design problems with my house which detract from the amazing view out of our front window. The biggest was that one quarter of the space in the house was taken up by a 'tuck under' garage. It was a 'heated garage' meaning that there was a heating circuit that sent hot water through radiators in the garage but it was still almost as cold as the outside temperatures. This garage was below my bedrooms! The floor of the bedrooms was freezing most of the Winter (which in Vermont starts in early November and ends in late March). The two nine foot wide and seven foot tall garage doors were a big part of the problem.

The task at hand

What to do about this house that hemorrhages heat in the heating season? The heat in the Summer was bearable for the most part, but we needed to do something about that heat loss!

The plan is to get rid of the garage doors, take the garage space and make it conditioned floor space. Then once that is done to super-insulate the house.  How to do this is part of the story of this blog. The rest of the blogs will be about my experiences on other high performance projects and energy audits of existing homes.

To bring yourself up to speed start off at my online blog at www.ecohousesofvt.com. After you are done with the last blog you can come back here for the continuation.

Thanks.

Chris!